Looking for a simple GPS to put on a foster dog that keeps going for runs....

There are a couple of ways to do this, you can use a 'GPS logger' to store a track of where the dog has been, this can only be examined when the dog returns (by connecting the logger to a computer), or you can get a 'pet / child tracker', this is similar to the logger but also has a cell phone built-in, you can call it for a current location or log into a website that is in contact with the tracker to see history track and current position, you can also set a 'zone' on a map and get the tracker to message you if the dog goes outside this area

The problem is that the batteries in a tracker won't last very long, so you would have to know when to activate it