My dog weighs 50 lbs, and I always use a retractable leash with him. But, I use one for his weight range. Nothing wrong with using a leash intended for a larger dog, but I really don't see the point. A leash made for the 20 lb range would be just fine. It takes a lot of force for them to break, my dog has used the same one for 2 years. The last one he had was cheap, and it only lasted for a few months before it wouldn't retract anymore. But, the line didn't break.