[WSSix]

Hidden kill switch that requires it be pressed or on to fire the starter or in your case, power the PCM. Using a relay system, you can make the kill switch many different things like a power window switch, cigarette lighter, or rear defrost switch etc. Use your imagination but make it something simple and convenient for yourself.

Removing the steering wheel is great.

Lastly, and this I believe is most important, accept the fact that if the car is wanted, it will be taken no matter what you do. Sorry. Carry good insurance on the car and park in safer areas whenever possible.