No chance of IP banning such individuals? Or perhaps frequently vandalised pages will need to be locked so that only registered users can edit them - that way you can track precisely who the offenders are and possibly ban them if you know who's doing it. I'm not sure how wikis work so I'm just assuming this based on what happens with message boards. The problem with IP banning are those really annoying pests who will move between internet cafés and troll from changing IP addresses (Japanese board trolls are notorious for doing this (-_-)).