I had a Tagg Pet Tracker for my dog when she was a puppy. Waterpoof (terminals will corrode some in salt water). It's wifi based so it only works in areas with good coverage. It also tracks slow so it doesn't tack like GPS. However, it lasts days to weeks within the area of the base station, send text notifications when taken out of the home wifi zone, and is trackable via an app tied to google maps with 30 second location updates based on nearest address.
Service was about $80 per year. I only stopped using it because she was rough housing with my parents dog, it came off, and subsequently got chewed up. She's yard trained and listens pretty well now so I didn't bother to replace it.
Edit: I forget why but I got it discounted in the Verizon showroom for $75 + tax. First 3 months of service was included.