the problem is that the legitimate GPS signal is ridiculously weak, and generally speaking, to reliably jam, you need a significantly stronger signal. (well, and compared to a solar-powered transmitter on a satellite, it's pretty hard not to have a significantly stronger signal) I'm not a RF guy myself, but I hang out with a bunch of them. Guaranteeing that your jammer only had a range of a few feet sounds... difficult.

I personally know people that have had problems with their systems that have been traced back to truckers with GPS jammers.