Okay, so the restrictions are held centrally rather than on the collar?<br/><br/>Hai, I have a suggestion: Use the mobile phone network. Your mobile service provider knows where you are (or at least where your phone is) to within a few hundred yards. In heavily populated areas they know to within a few feet. And this ability to track users pre-dates the GPS chips in phones. In fact, the GPS chip is really a passive thing that allows the phone to detect radio signals from satellites. It then triangulates it's position and displays that on the screen.<br/><br/>Unless the phone has special software installed, it does not transmit that location anywhere else.<br/><br/>On the other hand, every mobile phone transmits it's ID every few minutes to all the signal towers within range. These towers then transmit the phone's ID to a central computer that records the phone's ID and triangulates it's location.<br/><br/>The same system would work equally well for slave collars: they send a signal every few minutes giving the slave collar ID, to the mobile phone network. This is effectively a text message - it uses the data channel that all mobiles use to send texts.<br/><br/>Of course, out side of coverage, the collar would have to switch to the communication satellites that sat-phones use.<br/><br/>Note: GPS satellites don't receive, they only transmit!