Something which wasnt said before, the GPS is what it is: a GPS RECEIVER, it means, it only receives signals, it never submits any signal, it means that you cant use GPS to track a device, since the satelites only broadcast data, they dont receive anything back. In other words: you wont even be able to track it if its only 1 meter away....
for a bether understanding of how GPS receivers work you can follow this link: Howstuffworks "2-D Trilateration"
hope you learned something today