An interesting way to augment a fuel cutoff switch is with the seatbelt latch switch, so that BOTH the cutoff switch AND the seatbelt must be engaged. Since most theives won't buckle up before trying to start the car, they won't get anywhere, even if they find the "hidden" fuel switch.

You can modify the fuel cutoff scenario by having the fuel cutoff delayed by a timer, so that the engine gets fuel for 30 or 90 seconds before dying. They start the car, get it out on the road somewhere, but not very far away, and it dies. Now they are in the middle of traffic, and don't want to spend time "fixing" the problem, so they split. Since the car is probably in a non-normal spot, the police will become aware of it soon, and you will get notifed.

If you want to get fancy, have the fuel guage show an empty warning right away (before the timer kills the fuel flow), so they think the tank is really empty.