A unique id in forms could be an interesting way to avoid duplicates.

Each form in Savane would be created using a specific function.

When the user get the form : we add an entry (unique id, timestam).
Afer submission stage, the form is succesfull we remove it from db. If not, we keep it. If the entry is missing, we claim that the post was already registered.
To avoid keeping in database too old id, we'll remove with sv_cleaner every item older than 2 days ago (assuming that 2 days is a reasonnable amount of time to fill out of a form).