disable edit after a moderator edited a post

well, in my forum, right after our active moderators edit a message, the user edit it right after the mod, and they are playing a lil game, untill the 100 mints have passed, and the user cant edit his message no more. (my members hate this time limit for edit)
so please someone can make a hack that wont allow users to edit after a moderator edited thier message. (and moderator cant edit, after an admin moderated his message)
thanks in advance,
Shark.