have a alliance guage and when killing monsters your alliance goes up, if you pk someone, you get minus how much alliance they have, but if there alliance is negitive, you can kill then and you get alliance.
so people can pk pk\'ers without loosing alliance.
so if they want to pk someone, they have to be willing to spend time to get their alliance back up.
full alliance means you dont drop anything when you die, to discourage pking even more.
i gotta say this worked well in lineage, pking was open when you just need to shut up some fool,but pretty rare, if a pker showed up, everyone goes to town and warns everyone about him.
have guards in town.