How about:
Each time a person kills a player the reward on his head rises, depending on how much more lower level the char is than the pk\'er, the reward gets bigger.
Each pk adds to the total reward on his head. You then can keep track of who has got the biggest reward on his head on a webpage, wen the pk\'er is killed by someone this person gets the reward for killing the pk\'er and the reward on the pk\'er is reset then to half of the former reward. This way he still gets some heat, someone might try to take him out again for that 1/2 reward. Then the reward gets halved again and so on and so on. Their should also be some heavy penalty for a killed pk\'er, worse then normal, a big xp loss or he has to pay the reward? or ... Their should also be a way to get a pardon for an accidental pk then, pray in church during an hour(realtime) or something?
I think this system would be pretty nice cuz, newbies can be protected by people who hunt pk\'ers and get rewarded for this. And pk\'ers would love to get their name on top of the reward list(prestige).
Sekhmet