GPS is one-way though, your device isn’t sending anything up to the satellites, it’s just looking for where they are.

You still need a way to get a signal from the collar to your phone or computer or whatever device you’re using to track it. Things like airtags and tiles use Bluetooth to talk to nearby phones that relay it onto the Internet. If no one is close enough with a phone they’re basically useless, and if the cell service is spotty, the location can’t be updated until the phone has a signal, and depending on the area, that could be a while which means your dog could be miles from where they were when a phone last picked up the signal from their collar.

If the collar itself is hooked up to the cell network, then you don’t have to rely on someone being nearby with a phone to pick up the location, but it is still reliant on having cell service, which may not be a given if you’re out hiking in the mountains for example.

Other than that, you would have to use other satellite services, or rely on having a direct radio connection to the collar, sort of like a walkie talkie except carrying the GPS data instead of voice.