I did a little checking after I read a post about a GPS chip on the westiepoo. From what I understand and the info provided by GPS, they don't exist. It would be great if they did!
So if you were sold one or paid a premium for a GPS tracking chip-you may want to try to get your money back.
There are a few other types of chips-not tracking-just ID and can be scanned and owner located if the dog is lost. I highly recommend them, especially if you live in a highly populated area. In some cases it is the only way that dogs who lose their tags and collars are reunited with the owners. Some brands include-Avid, Homeagain and a few other not as well known brands.

Here's one link that I found. They sound pretty big and I'm sure very expensive for the prototypes. I think they are still in the testing stage-even though this is an older press release.
http://adsx.com/news/2003/051303.html

I first began working with Global Positioning Satellite system receivers back in 1992. The units back then had a "harness" of sorts...was part of my profession..mapping extractive resource lands..natural gas/oil. These receivers were larger than a clipboard and a heck of a lot heavier, made for a darn long day when it was 105 out. That being said wait. Look at size of GPS receivers now, size of a deck of cards, sometimes smaller. Military has all kinds of fun, technical stuff..you'll see. Technology seems to "double" every year or so. A pacemaker isn't so small. Think what we'll have in 5 years. Think the quality/price of digital cameras and computer equipment past 5 years. I would be skeptical if I owned the "present technology"...not talking microchips. e

Sorry my post contained an insensitive passage. Military hardly means fun, sure friendships are one thing, seeing the world another appropriate one. I've been there, the word "fun" is incorrect. Technology that will come out of contracts and declassification is another factor that "could" work for us, though with this I see a lot of Big Brother applications for better or worse. Its an ambigious world/state/planet/county.