they're getting bored it sounds like.. maybe perhaps look into getting interactive games like Trivia, hangman, etc that can be played while the channel chatter isn't entertaining enough. Get to the root of the problem to solve it =)
Check out
www.mirc.net, www.mircscripts.org,
www.hawkee.com and other mIRC sites for scripts/addons that will have games.
But a limit on the triggers WOULD be a good thing to have regardless. The thread that was pointed out that is about text flood discusses the problem and has a few methods of approaching it.
