Tortoise Tracking Device

I spent part of the day looking for a tortoise tracking device. It's hard. Almost all work on your smart phone but if you don't get phone coverage, which you don't out here, it's useless. Plus you can't put them on their inside and on the outside it will get peeled off or disappear when he goes down in his house. I did find a couple possibilities I'm doing more research on but these aren't them.