Cloaca
I know plenty of us have had people that like to teleport kill, so I suggest making it so that if you're in the actual pk arena (not standing outside of it), that the Z function to teleport would be disabled. The only way to leave the arena at that point would be to die and teleport from the outside, or use the longer teleport to town skill, which is in the Motion menu (o). This should easily get rid of teleport killers.