What about making an open bounty for killing them? Paying out individual bounties might be a PITA, but you’d only be paying for results (I suppose you could require that they must submit at least x kills at a time). It also might be more effective, as this conceivably get more people into hunting them. I mean, adding bounties on top of loot drops and ESS thefts might make them a juicy target to a lot of players.