diff --git a/app/models/bookmark.rb b/app/models/bookmark.rb
index 75e47a37f..d626e5c67 100644
--- a/app/models/bookmark.rb
+++ b/app/models/bookmark.rb
@@ -24,14 +24,17 @@ class Bookmark < Content
   belongs_to :owner, class_name: 'User'
 
   validates :title,     presence: { message: "Le titre est obligatoire" },
-                        length: { maximum: 100, message: "Le titre est trop long" }
+                        length: { maximum: 100, message: "Le titre est trop long" },
+                        uniqueness: { message: "Un lien avec le même titre a déjà été proposé" }
   validates :link, presence: { message: "Vous ne pouvez pas poster un lien vide" },
                    http_url: { message: "Le lien n'est pas valide" },
-                   length: { maximum: 255, message: "Le lien est trop long" }
+                   length: { maximum: 255, message: "Le lien est trop long" },
+                   uniqueness: { message: "Le lien a déjà été proposé" }
+  validates :lang, inclusion: { in: Lang.valid_codes, allow_nil: false, message: "La langue du lien doit être définie" }
 
   def link=(raw)
     raw.strip!
-    return write_attribute :url, nil if raw.blank?
+    return write_attribute :link, nil if raw.blank?
     uri = URI.parse(raw)
     # Default to HTTP link if neither scheme nor host is found
     if uri.scheme.blank? && uri.host.blank?
diff --git a/app/models/lang.rb b/app/models/lang.rb
index 28c682fa5..6d3e5a30b 100644
--- a/app/models/lang.rb
+++ b/app/models/lang.rb
@@ -8,6 +8,10 @@ def self.all
     vals.zip(keys)
   end
 
+  def self.valid_codes
+    $redis.lrange("lang", 0, -1).difference(["xx"])
+  end
+
   def self.[]=(key, value)
     $redis.set("lang/#{key}", value)
     $redis.rpush("lang", key)
diff --git a/app/models/link.rb b/app/models/link.rb
index 52fde9b42..a8e091227 100644
--- a/app/models/link.rb
+++ b/app/models/link.rb
@@ -25,10 +25,12 @@ class Link < ActiveRecord::Base
   Accessible = [:id, :user, :title, :url, :lang]
 
   validates :title, presence: { message: "Un lien doit obligatoirement avoir un titre" },
-                    length: { maximum: 100, message: "Le titre est trop long" }
+                    length: { maximum: 100, message: "Le titre du lien est trop long" }
   validates :url, http_url: { protocols: PROTOCOLS, message: "L'adresse n'est pas valide" },
                   presence: { message: "Un lien doit obligatoirement avoir une adresse" },
                   length: { maximum: 255, message: "L’adresse est trop longue" }
+  validates :lang, inclusion: { in: Lang.valid_codes, allow_nil: false, message: "La langue du lien doit être définie" }
+
 
   def url=(raw)
     raw.strip!
diff --git a/app/models/news.rb b/app/models/news.rb
index 67d5f4a45..cd6b91d59 100644
--- a/app/models/news.rb
+++ b/app/models/news.rb
@@ -50,6 +50,8 @@ class News < Content
     dependent: :destroy,
     inverse_of: :news
 
+  validates_associated :section, message: "Veuillez choisir une section pour cette dépêche"
+
   scope :sorted,    -> { order(updated_at: :desc) }
   scope :draft,     -> { where(state: "draft").includes(node: :user) }
   scope :candidate, -> { where(state: "candidate") }
diff --git a/app/models/post.rb b/app/models/post.rb
index 9b89706c9..7740a3062 100644
--- a/app/models/post.rb
+++ b/app/models/post.rb
@@ -23,6 +23,8 @@ class Post < Content
 
   belongs_to :forum
 
+  validates_associated :forum, message: "Vous devez choisir un forum" 
+
   scope :with_node_ordered_by, ->(order) { joins(:node).where("nodes.public = 1").order("nodes.#{order} DESC") }
 
   validates :forum,     presence: { message: "Vous devez choisir un forum" }
diff --git a/app/models/tracker.rb b/app/models/tracker.rb
index f172cafd4..f51216404 100644
--- a/app/models/tracker.rb
+++ b/app/models/tracker.rb
@@ -28,10 +28,13 @@ class Tracker < Content
   belongs_to :assigned_to_user, class_name: "User"
   belongs_to :category
 
+  validates_associated :category, message: "Veuillez choisir une catégorie pour cette entrée de suivi"
+
   attr_accessor :pot_de_miel
 
   validates :title,     presence: { message: "Le titre est obligatoire" },
                         length: { maximum: 100, message: "Le titre est trop long" }
+  validates :category,  presence: { message: "Veuillez choisir une catégorie pour cette entrée de suivi" }
   validates :wiki_body, presence: { message: "Veuillez décrire cette entrée du suivi" }
 
   scope :opened, -> { where(state: "opened") }
diff --git a/app/views/bookmarks/_form.html.haml b/app/views/bookmarks/_form.html.haml
index 5c94b3a65..035bcd0b4 100644
--- a/app/views/bookmarks/_form.html.haml
+++ b/app/views/bookmarks/_form.html.haml
@@ -8,7 +8,7 @@
   = form.text_field :link, autocomplete: 'off', required: 'required', spellcheck: 'false', maxlength: 1024
 %p
   = form.label :lang, "Langue"
-  = form.select :lang, Lang.all
+  = form.select :lang, Lang.all, { include_blank: true }, { required: "required" }
 %p
 - if form.object.new_record?
   %p
@@ -16,4 +16,4 @@
     = text_field_tag :tags, nil, class: 'autocomplete', 'data-url' => autocomplete_tags_path, value: params[:tags], size: 100
 %p
   = form.submit "Prévisualiser", id: "bookmark_preview"
-  = form.submit "Poster le lien", 'data-disable-with' => "Enregistrement en cours" if @preview_mode
+  = form.submit "Poster le lien", 'data-disable-with' => "Enregistrement en cours" if @preview_mode and @bookmark.valid?
diff --git a/app/views/bookmarks/edit.html.haml b/app/views/bookmarks/edit.html.haml
index d4f196aae..ec9978046 100644
--- a/app/views/bookmarks/edit.html.haml
+++ b/app/views/bookmarks/edit.html.haml
@@ -1,7 +1,7 @@
 %main#contents(role="main")
   =h1 "Éditer un lien"
 
-  = render "preview", preview: @bookmark if @preview_mode
+  = render "preview", preview: @bookmark if @preview_mode and @bookmark.valid?
 
   %h2 Édition
   = form_for [@bookmark.owner, @bookmark] do |form|
diff --git a/app/views/bookmarks/new.html.haml b/app/views/bookmarks/new.html.haml
index 6cef285b9..bfd923406 100644
--- a/app/views/bookmarks/new.html.haml
+++ b/app/views/bookmarks/new.html.haml
@@ -9,7 +9,7 @@
   %p
     Les <a href="/regles_de_moderation">règles de modération</a> sont applicables aux liens comme au reste du site.
 
-  = render "preview", preview: @bookmark if @preview_mode
+  = render "preview", preview: @bookmark if @preview_mode and @bookmark.valid?
 
   = form_for @bookmark do |form|
     = render form
diff --git a/app/views/comments/_form.html.haml b/app/views/comments/_form.html.haml
index c27164075..d95b70a57 100644
--- a/app/views/comments/_form.html.haml
+++ b/app/views/comments/_form.html.haml
@@ -8,4 +8,4 @@
   = form.text_area :wiki_body, required: 'required', spellcheck: 'true', class: 'markItUp', placeholder: "Vous pouvez écrire votre commentaire ici.\n\nMerci de rester poli et courtois, on compte sur vous !"
 %p
   = form.submit "Prévisualiser", id: "comment_preview"
-  = form.submit "Poster le commentaire", 'data-disable-with' => "Enregistrement en cours" if @preview_mode
+  = form.submit "Poster le commentaire", 'data-disable-with' => "Enregistrement en cours" if @preview_mode and @comment.valid?
diff --git a/app/views/comments/edit.html.haml b/app/views/comments/edit.html.haml
index 2b068a3b2..02ec847c6 100644
--- a/app/views/comments/edit.html.haml
+++ b/app/views/comments/edit.html.haml
@@ -2,7 +2,7 @@
   =h1 "Éditer un commentaire"
 
   %div#comments
-    = render "preview", preview: @comment if @preview_mode
+    = render "preview", preview: @comment if @preview_mode and @comment.valid?
 
   = form_for [@comment.node, @comment] do |form|
     = render form
diff --git a/app/views/comments/new.html.haml b/app/views/comments/new.html.haml
index cd2626bb6..8e99ffabc 100644
--- a/app/views/comments/new.html.haml
+++ b/app/views/comments/new.html.haml
@@ -18,7 +18,7 @@
   - else
     = render @comment.node.content
     %div#comments
-      = render "preview", preview: @comment if @preview_mode
+      = render "preview", preview: @comment if @preview_mode and @comment.valid?
 
   = form_for [@node, @comment], url: "/nodes/#{@node.id}/comments#comment_new" do |form|
     = form.hidden_field :parent_id
diff --git a/app/views/diaries/_form.html.haml b/app/views/diaries/_form.html.haml
index c4dcd6eed..fd8ceae89 100644
--- a/app/views/diaries/_form.html.haml
+++ b/app/views/diaries/_form.html.haml
@@ -15,4 +15,4 @@
     = form.label :cc_licensed, 'Je place ce document sous licence Creative Commons Attribution et Partage dans les mêmes conditions, version 4.0 (<a href="http://creativecommons.org/licenses/by-sa/4.0/deed.fr">licence CC By‑SA 4.0</a>)'.html_safe
 %p
   = form.submit "Prévisualiser", id: "diary_preview"
-  = form.submit "Poster le journal", 'data-disable-with' => "Enregistrement en cours" if @preview_mode
+  = form.submit "Poster le journal", 'data-disable-with' => "Enregistrement en cours" if @preview_mode and @diary.valid?
diff --git a/app/views/diaries/edit.html.haml b/app/views/diaries/edit.html.haml
index be5d75ac3..a29f74f91 100644
--- a/app/views/diaries/edit.html.haml
+++ b/app/views/diaries/edit.html.haml
@@ -1,7 +1,7 @@
 %main#contents(role="main")
   =h1 "Éditer un journal"
 
-  = render "preview", preview: @diary if @preview_mode
+  = render "preview", preview: @diary if @preview_mode and @diary.valid?
 
   %h2 Édition
   = form_for [@diary.owner, @diary] do |form|
diff --git a/app/views/diaries/new.html.haml b/app/views/diaries/new.html.haml
index f9a4e75aa..ef40e25c4 100644
--- a/app/views/diaries/new.html.haml
+++ b/app/views/diaries/new.html.haml
@@ -4,7 +4,7 @@
   %p
     Des <a href="/regles_de_moderation">règles de modération</a> sont applicables aux journaux (et au reste du site).
 
-  = render "preview", preview: @diary if @preview_mode
+  = render "preview", preview: @diary if @preview_mode and @diary.valid?
 
   = form_for @diary do |form|
     = render form
diff --git a/app/views/news/_form.html.haml b/app/views/news/_form.html.haml
index 845e91081..a073f603e 100644
--- a/app/views/news/_form.html.haml
+++ b/app/views/news/_form.html.haml
@@ -16,7 +16,7 @@
   = form.text_field :title, autocomplete: 'off', required: 'required', spellcheck: 'true', maxlength: 100
 %p
   = form.label :section_id, "Section de la dépêche"
-  = form.collection_select :section_id, Section.published, :id, :title
+  = form.collection_select :section_id, Section.published, :id, :title, { include_blank: true }, { required: "required" }
 %p
   = form.label :wiki_body, "Contenu de la dépêche"
   = form.text_area :wiki_body, required: 'required', spellcheck: 'true', class: 'markItUp'
@@ -51,4 +51,4 @@
   = form.label :cc_licensed, 'Je place ce document sous licence Creative Commons Paternité - Partage des conditions initiales à l’identique, version 4.0 (<a href="http://creativecommons.org/licenses/by-sa/4.0/deed.fr">licence CC By-SA 4.0</a>). Ceci est conseillé afin de permettre l’édition coopérative de la dépêche si elle doit être complétée.'.html_safe
 %p
   = form.submit "Prévisualiser", id:  "news_preview"
-  = form.submit "Soumettre cette dépêche", 'data-disable-with' => "Enregistrement en cours" if @preview_mode
+  = form.submit "Soumettre cette dépêche", 'data-disable-with' => "Enregistrement en cours" if @preview_mode and @news.valid?
diff --git a/app/views/news/new.html.haml b/app/views/news/new.html.haml
index 85230fc21..409c56e3d 100644
--- a/app/views/news/new.html.haml
+++ b/app/views/news/new.html.haml
@@ -11,7 +11,7 @@
       = list_of(news) do |news|
         = link_to news.title, [:redaction, news]
 
-  = render "preview", preview: @news if @preview_mode
+  = render "preview", preview: @news if @preview_mode and @news.valid?
 
   = form_for setup_news(@news), url: '/news' do |form|
     = render form
diff --git a/app/views/polls/_form.html.haml b/app/views/polls/_form.html.haml
index 19099b997..afd45f82c 100644
--- a/app/views/polls/_form.html.haml
+++ b/app/views/polls/_form.html.haml
@@ -14,4 +14,4 @@
       = aform.text_field :answer, maxlength: 128, size: 30
 %p
   = form.submit "Prévisualiser", id: "poll_preview"
-  = form.submit "Proposer ce sondage", 'data-disable-with' => "Enregistrement en cours" if @preview_mode
+  = form.submit "Proposer ce sondage", 'data-disable-with' => "Enregistrement en cours" if @preview_mode and @poll.valid?
diff --git a/app/views/polls/new.html.haml b/app/views/polls/new.html.haml
index e20def975..3763d2540 100644
--- a/app/views/polls/new.html.haml
+++ b/app/views/polls/new.html.haml
@@ -4,7 +4,7 @@
   %p
     Des <a href="/regles_de_moderation">règles de modération</a> sont applicables aux sondages (et au reste du site).
 
-  = render "preview", preview: @poll if @preview_mode
+  = render "preview", preview: @poll if @preview_mode and @poll.valid?
 
   = form_for setup_poll(@poll) do |form|
     = render form
diff --git a/app/views/posts/_form.html.haml b/app/views/posts/_form.html.haml
index 3439666d7..0ad198913 100644
--- a/app/views/posts/_form.html.haml
+++ b/app/views/posts/_form.html.haml
@@ -15,4 +15,4 @@
     = text_field_tag :tags, nil, class: 'autocomplete', 'data-url' => autocomplete_tags_path, value: params[:tags], size: 100
 %p
   = form.submit "Prévisualiser", id: "post_preview"
-  = form.submit "Poster le message", 'data-disable-with' => "Enregistrement en cours" if @preview_mode
+  = form.submit "Poster le message", 'data-disable-with' => "Enregistrement en cours" if @preview_mode and @post.valid?
diff --git a/app/views/posts/edit.html.haml b/app/views/posts/edit.html.haml
index 5bda1c196..7f37214af 100644
--- a/app/views/posts/edit.html.haml
+++ b/app/views/posts/edit.html.haml
@@ -1,7 +1,7 @@
 %main#contents(role="main")
   =h1 "Éditer un message"
 
-  = render "preview", preview: @post if @preview_mode
+  = render "preview", preview: @post if @preview_mode and @post.valid?
 
   %h2 Édition
   = form_for [@forum, @post] do |form|
diff --git a/app/views/posts/new.html.haml b/app/views/posts/new.html.haml
index d54158e9a..c97e44a1a 100644
--- a/app/views/posts/new.html.haml
+++ b/app/views/posts/new.html.haml
@@ -4,7 +4,7 @@
   %p
     Des <a href="/regles_de_moderation">règles de modération</a> sont applicables aux forums (et au reste du site).
 
-  = render "preview", preview: @post if @preview_mode
+  = render "preview", preview: @post if @preview_mode and @post.valid?
 
   = form_for @post, url: "/posts" do |form|
     = render form
diff --git a/app/views/trackers/_form.html.haml b/app/views/trackers/_form.html.haml
index aac89aba8..4015bc3d8 100644
--- a/app/views/trackers/_form.html.haml
+++ b/app/views/trackers/_form.html.haml
@@ -5,7 +5,7 @@
   = form.text_field :title, autocomplete: 'off', required: 'required', spellcheck: 'true', maxlength: 100
 %p
   = form.label :category_id, "Catégorie"
-  = form.collection_select :category_id, Category.all, :id, :title
+  = form.collection_select :category_id, Category.all, :id, :title, { include_blank: true }, { required: "required" }
 - if @tracker.new_record?
   %p.pot_de_miel
     = form.label :pot_de_miel, "Ne pas remplir ce champ"
@@ -23,4 +23,4 @@
       = form.collection_select :assigned_to_user_id, Account.tracker_admin, :user_id, :login, include_blank: true
 %p
   = form.submit "Prévisualiser", id: "tracker_preview"
-  = form.submit "Soumettre", 'data-disable-with' => "Enregistrement en cours" if @preview_mode || @tracker.persisted?
+  = form.submit "Soumettre", 'data-disable-with' => "Enregistrement en cours" if (@preview_mode || @tracker.persisted?) and @tracker.valid?
diff --git a/app/views/trackers/edit.html.haml b/app/views/trackers/edit.html.haml
index db7f0eebd..c131a4717 100644
--- a/app/views/trackers/edit.html.haml
+++ b/app/views/trackers/edit.html.haml
@@ -1,7 +1,7 @@
 %main#contents(role="main")
   =h1 "Modifier une entrée dans le suivi"
 
-  = render "preview", preview: @tracker if @preview_mode
+  = render "preview", preview: @tracker if @preview_mode and @tracker.valid?
 
   %h2 Édition
   = form_for @tracker do |form|
diff --git a/app/views/trackers/new.html.haml b/app/views/trackers/new.html.haml
index d2e4a9325..7981dea75 100644
--- a/app/views/trackers/new.html.haml
+++ b/app/views/trackers/new.html.haml
@@ -4,7 +4,7 @@
   %p
     Il s’agit du suivi des suggestions et bogues concernant le site LinuxFr.org.
 
-  - if @preview_mode
+  - if @preview_mode and @tracker.valid?
     = render "preview", preview: @tracker
   - else
     = image_tag "/images/dessins/geekscottes_068.png", alt: "Tu coderas pour moi !", title: "Tu coderas pour moi ! — © Johann « nojhan » Dréo, 7 novembre 2007 — Licence CC‑By‑SA 2.5"
diff --git a/app/views/wiki_pages/_form.html.haml b/app/views/wiki_pages/_form.html.haml
index ef2144de2..c7ae7db63 100644
--- a/app/views/wiki_pages/_form.html.haml
+++ b/app/views/wiki_pages/_form.html.haml
@@ -6,4 +6,4 @@
   = form.text_field :message, autocomplete: 'off', spellcheck: 'true', maxlength: 250, size: 80
 %p
   = form.submit "Prévisualiser", id: "wiki_preview"
-  = form.submit (form.object.new_record? ? "Créer" : "Mettre à jour") if @preview_mode
+  = form.submit (form.object.new_record? ? "Créer" : "Mettre à jour") if @preview_mode and @wiki_page.valid?
diff --git a/app/views/wiki_pages/edit.html.haml b/app/views/wiki_pages/edit.html.haml
index 58eaeda01..ea741db14 100644
--- a/app/views/wiki_pages/edit.html.haml
+++ b/app/views/wiki_pages/edit.html.haml
@@ -1,7 +1,7 @@
 %main#contents(role="main")
   =h1 "Modifier une page de wiki"
 
-  = render "preview", preview: @wiki_page if @preview_mode
+  = render "preview", preview: @wiki_page if @preview_mode and @wiki_page.valid?
 
   = form_for @wiki_page do |form|
     = messages_on_error @wiki_page
diff --git a/app/views/wiki_pages/new.html.haml b/app/views/wiki_pages/new.html.haml
index 1348cf479..7451d3b2e 100644
--- a/app/views/wiki_pages/new.html.haml
+++ b/app/views/wiki_pages/new.html.haml
@@ -4,7 +4,7 @@
   %p
     Des <a href="/regles_de_moderation">règles de modération</a> sont applicables aux pages du wiki (et au reste du site).
 
-  = render "preview", preview: @wiki_page if @preview_mode
+  = render "preview", preview: @wiki_page if @preview_mode and @wiki_page.valid?
 
   = form_for @wiki_page do |form|
     = messages_on_error @wiki_page