I think that there should be a universal system where divers have a beacon on their dive flag and if a boat gets within 50 meters of it their engine slows to a crawl. The idea has lots of flaws, but it would save lives if it could be figured out.
Thats a pretty good idea! Have you ever seen the bait cars that police use? The carjackers steal the car and when the police get to the scene they are able to shut the car down.
Or maybe just one of those EMP things would do the trick:martial