A suggestion for the new forum website:
[Option A] If the last post is under the same name as the user trying to post, warn the user of double posting and optionally show a message saying "Please use the edit button unless you intend to bump this topic". Also user should be able to opt out these warnings in their profile settings. Getting the warnings until it annoys them should get the point across.
[Option B]
F1r3tar wrote:
Why not just develop or implement a plugin (for lack of a better word) that merges a double post into one post? I've seen this on Xenforo software, so it's not impossible to do.