Fenton,
I've seen people using those before. I wish there was some way to try one without buying one. My dog is not even two yet and pulls like mad. He only weighs 75 lbs, but it is all muscle. He has pulled my wife off her feet before and almost got me one day when he saw a squirrel across the road and made a right angle course change in a split second. Maybe in another 6 months or so it may be safe to hook him to the bike.