Sounds like you may need to do some house cleaning. You should develop an absolutely no exception to the rule, no tolerance policy. If someone is caught underage drinking or pre partying or switching bands (which is ILLEGAL!) they need to get the boot. The severity of the situation needs to be made in plain terms. "Either we shape up or we ship out. If we get kicked off campus, it looks bad for our organization as a whole. etc." You may end up with a lot fewer members, but your organization will still exist on your campus and you can start from scratch. I know, easier said than done. Hope this helps some.