Seeing as it's a Clifford Concept it will go off pretty much constantly anyway (as most owners seem to set the proximity to within about half a mile!) and so when it goes off for real everyone will just ignore it and the thief will get away.

Fit a Snap-off steering wheel boss, IMO a car without a steering wheel is just about the best deterrent there is. Sure they could trailer away, but a very small percentage of thieves work that way.