Cut the little wire that goes to the stop solenoid on the back of the injection pump run one side of the cut wire to a switch and from the other side of the switch back to the solenoid.Fancy explaining just how easy it is ?
You would be better fitting some sort of fuel cut off switch so would start and die after 20 seconds or so if tampered with, and of course the thief is not going to mess around on the side of the road with a dead stolen car.
Electric 12v Fuel CUT-OFF Solenoid Valve - 6.0mm dia on eBay (end time 22-Mar-11 21:39:55 GMT)
Lynall