I dont really fault authorities or the schools for not prosecuting when in many cases the "victim" has no idea what happened. You can't bring a case for trial when the "victim" doesn't know where she was, what she did or if she consented or not. I'm not saying its right but once alcohol and drugs get involved the likelihood of prosecution almost completely collapses.
in order to prevent these acts you need to start with telling girls to avoid overindulging and use the buddy system....you get past those two steps and it turns into mystery land. Yeah it shouldn't be the girls responsibility, guys are pigs, blah blah but if you want to solve the problem sometimes you gotta take it upon yourself to do so.