Can anyone recommend a really good, reliable GPS tracker system you have used with your dog, that covers a decent distance (in case of loss/theft), is easy enough to use etc? Obviously not wanting to pay the earth, but cost isn't TOO much of an issue as this will be for my partner's birthday present. (Dog is with him most of the time). It needs to be compatible with iPhone, as that is what he has, and I really want one where you pay fully upfront rather than a monthly subscription, if that is possible? So grateful if anyone can help!