One of my dogs can get out anywhere. We have tried putting things around the base of our chain link fence and even tying the fence down but nothing works. He just goes right under or digs right through. He has an id on his collar so luckily people call when they find him, but I'm worried he'll get hit by a car. Anyway, has anyone tried those underground electric fences and will it hurt him? He's about 20 lbs, so he's not too little.