I'm not crazy about invisible fences. Dogs can learn to hear the beep, there's a moments pain, and then they're free!

For tangling, try using a 6' chain (they don't tighten up as bad when the dog is tangled), and put it on a tall post. I'd say 3' minimum if you're in a low snow area. This helps keep the chain off of the ground, and makes it harder for the dog to get tangled .