That’s actually a really big concern for trackers who run “off lead” and why many folks won’t do it. I’ve heard stories of several dogs being run over just this year. The Garmin Alpha Unit is a pretty new setup I believe. I think it’s only been out a few years and it seems to just be catching on amongst the tracking community. Up until it came out I think the only way to call your dog back was with a whistle or voice command. The bad thing about that though is that a dog, especially a young one, still has the choice to obey or not. When the dogs get their prey drive triggered or they get really into the tracking…..it becomes a lot harder to get them to listen to you. I saw that with Otis when he would get after squirrels here at the house and why I was very nervous to track off lead. With that Alpha Unit though, you can control the dog out to long distances and the ones I’ve seen worked on it don’t even question it for a second. It’s about like having push button brakes on your dog.