[MarkFL]

Create a plugin hooked at "newpost_process" with the following Plugin PHP Code:

Block Disabled:      (Update License Status)
Suspended or Unlicensed Members Cannot View Code.

What this does is if "http://" is embedded in the thread title, the content of the post will be erased, and the user will be told their post is too short.

--------------- Added 05 Oct 2016 at 20:10 ---------------

A more complete solution can be found here:

Block Censored Words in Posts by BOP5 VB4

This product will allow you to check post titles/content for additionally censored words/strings. You can specifiy which forums in which it is active too.