Making a car difficult to steal

Yea my first choice is magnavolt.

I reckon the second (unfortunately magnavolt is not legal yet) is the outstanding post about the fuel cut-off solenoid. Wow, they get it running, pull out on the highway or the road and stall permanently. That attracts attention there.

I always thought about running the key like standard but also having a secondary switch that needed to be actuated as well to unground the coil negative side. That way it just wont run when switch is closed to ground.