I recently found a small GPS tracker that works via GSM and text messaging to control and get location updates. Now I have Border Terrier that I dont want to loose but can't justify a full blown GPS tracking collar solution. So for £20 and a pay as you go SIM has me a very small tracker that I can attach to his collar or harness. I can then send it an sms text and within seconds it sends me back a text with lat lon coordinates and a link to google maps to pinpoint him on a map. I also found a mapping / tracking software that I have loaded onto my phone and automatically reads the text and puts his position on a map.
Only works with GSM coverage but if lost your dog is more than likely return to some coverage and the tracker report back. The tracker is about the size of a box of matches and from my tests so far is very accurate.
May be of interest to others looking for a simple cost effective tracker solution.