I read a story some years back about how people were dealing with car thieves and carjackers in the new South Africa, where the crime rate is so high the actual numbers are regarded as a state secret.
Some have installed side-firing flamethrowers on their cars, some have spring loaded sword blades that come out from underneath, but the cheapest solution was a guy who kept a bottle of brandy he'd laced with either cyanide or arsenic in his glove box, figuring whoever stole the car would find the booze and drink up.
In the USA, doing any of these could get you in MORE trouble than the car thief. Clearly the flamethrower/sword ideas, being mechanical installations, are booby traps of your doing, banned in most states. If the authorities could conclusively link you despite your denials to poison booze via fingerprints on the bottle or something, you wouldn't duck legal trouble there, either. Don't get caught doing something like this.