A GPS tracker for dogs is a totally legal way to keep tabs on your fluffy buddy, at least here in the States. In fact, a lot of owners find them a very useful addition to microchips because they don't require that someone take your puppy in to see a vet before he can be identified. In Canada and New Zealand, as well as some other countries, there may be different restrictions. It's best that you check online with your local authorities, first!