Best Option for last
Fifteen years ago I spliced into the starter line. Put a $2 Radio Shack rocker switch in the plastic panel along side of the rear seat but below seat level so it can be felt but not seen. Kills the starter, easy to reach unobserved when leaving the car. Another person did the same but disabled the cigarette lighter mechanism and set it up so that when the lighter was in, the switch was thrown and the car would start.
Lastly, a number of years ago, Kirban sold a switch with a relay. To operate the relay and close the switch, a circuit needed to be connected and he recommended two screws of your choice that when you touched both, would complete the circuit and close the relay.
Of course, none of these stop the tow truck so I recommend that you garage the car. One person at a show told me that in one case, they broke open the garage to get the car so I also recommend that you have your wife sleep in the car. It is my thinking that if they get my car, they also get my wife as well, so it is not a complete loss.