Many years ago, some guys who were involved here split off into another site called Renderotica (no links, please) in an attempt to address this issue. I agree with that approach: render unto the adult site that which is adult content. People will still try to post such items here, but maybe it's because they don't know about the adult site. Enforcement will always seem uneven and unfair, but it's actually complaint-based. If they don't see it and don't know about it, they can't enforce anything.