I apologize that I don’t really have an answer for this but I can only read this title in Skwisgaar’s voice now.

Serious answer: prediction markets. People bet on the time of death of the victim. The person that bets the closest to the actual time of death wins. A would be assassin would theoretically always know the exact moment of the attempt on this persons life.

Hiring a bounty hunter to take out the bounty hunter you hired to take out the bounty hunter…

You get the idea.

The devil is in the details, isn’t it?

It’s usually the job of governments to enforce agreements. If you take them out, then you’re on your own.