I think each player should have a kill count. When you kill a player, the kill count goes up, unless the player you killed flagged combat first, ingame you should be able to see the players name, if its Red they are murderer, grey criminal, blue = innocent.
The kill counts should go down as time goes on, like 2 hours per kill, or 3, or something like that.

There should be \"safe\" zones, and non safe zones... like cities would have guards that would kill the criminals/murderers if they see them, or a person can call the guards to have the person killed.

I think that PK, and PvP is an essential part to any MMORPG... it makes it more exciting to go outside of the cities barriers... theres always a chance of death, and harm... and thats what makes an adventure and adventure... The fear and thrill of knowing you are in danger at all times....

In town, they can have the safe feeling where they know they arent going to be harmed... but once you venture outside of the cities walls.... the adventure begins


ALSO: This solves any problems with tons of PK\'s... if they cannot enter town- how are they going to get their items? they are going to die... a lot... and if you make it hard to be a PK, hard to get items... get resurrected... enter towns... outcastish... there wont be that many..