Take their assets and put $10M towards keeping the bounty program going. Take another $15M and put it towards a second (even bigger) bounty. Every day a billionaire’s name gets lottery’ed and killing them wins the big pot plus the original $10M bounty. So every single billionaire has a constant bounty on them, but at first it may only be $25M. But as more and more die, that bigger pot continues to grow.

Their private security teams may not be willing to turn against their masters for only $10M… But for $25M? $40M? $55M? $70M? Everyone has a price, especially the billionaires’ mercenaries. Of course, the billionaires would probably start requiring bomb collars for their private security at that point, to ensure they remain loyal. But that means the teams would inevitably weigh the price of a bomb collar vs an easy $10M payout in the first place. And that $10M alone would be enough to have them gunning down the billionaires before they put the collars on.