[Lord Warlock]

agree, a short wire to the starter solenoid wire that opens the circuit till the switch is used will keep someone from starting the car...unless they push start it. Easy to conceal, a small toggle under the dash or better yet, use an old switch not used anymore such as the active exhaust button (if you've put an aftermarket exhaust on it) or even sneakier, the window lock button on the drivers door, a totally useless button to start with.