I'm not a gadget girl but I do love GPS trackers for dogs. We use them all the time, both for boarding dogs and for our own nose-to-the-ground hunting dog, Perro. Anyone who has ever walked a dog understands the fear when they disappear. We know they need to explore and sniff and have fun and be free, but it is terrifying when they are out of sight, even for a few minutes. And of course they should be trained so that they return immediately on command, but even the most perfect dog becomes selectively deaf from time to time.
We have trialled a number of tracker types over the past few years and the one we are most pleased with is the Tractive brand. The Tractive trackers are waterproof (not always the case with other brands as we learned to our cost...), neat and unobtrusive, come with 2 casing widths to fit on either thin or thicker collars, not too expensive (about €80/year) and, importantly for us, the customer service is excellent. When one of our trackers got damaged recently. it was replaced quickly and free of charge (we took their insurance for lifetime replacement and we're glad we did). If you'd like to order a tracker, the company have a refer a friend scheme offering the purchaser a 15% discount and the referrer a month free on their own subscription plan - here's the code and happy wandering!