i think the most affective way is not to restrict boys, but to delete nasty/sexual comments as soon as they are posted up. admittedly boys know more about computers than girls do, they know how to tweak the gender and stuff and still write sexual crap in guise as girls. Maybe can set up a new post for girls to complain about ppl who comment bad stuff and request for it to be taken down, as well as to suspend the person from GC for a few weeks?