Making a car difficult to steal

I built an ignition kill switch using a relay and the wiper sprayer switch. Run a live wire to the relay and the relay controls the ignition start circuit. Put a jumper switch under the dashboard to defeat it intentionally when you drop it off for service.

When starting the car, hold the wiper spray switch in while turning the key to crank. This will not defeat a guy who knows how to hot wire the ignition.