I have heard that in some parts of the US (and im from canada so dont make fun of me if you cant find it) they have tiny tracking devices the size of the tags you insert into an animals neck. like a little pill size and have seen it used on many crime shows such as CSI and whatnot but i have only heard of them used on humans. im sure if you could track it down it wouldnt be hard to have the vet insert it the same way as the ID chips.
there are also collars (leg bands for humans as well) that you can purchase. just google Tracking Devices...better yet...Ebay it
The implant chips are not for tracking but only work for identifying. If you search for tracking devices/collars all you get are ones for dogs and other large animals that have a range of several miles. I'm looking for something smaller with much less range (AND less costly!).
Hmm... I've seen something in Cat Fancy magazine that is a collar and it has a tracking device on it, but I think the price was a bit expensive. I don't know the website though. I'll see if I can find the web address later if there is one.