William Koehler was a dog trainer who started using long thin leads for dog obedience training. I like using a long lead, but not a thin one. I think a long lead is one of the most dangerous things you can use in dog training, particularly with large dogs like Shepherds. You can break or lose a finger with one of these before you know it. It takes practice, practice, practice before you are comfortable using this kind of lead. The lead I use is 30 feet long, but I use that when my dog is doing a search and I don’t want him off lead. Whatever you do, do not use one of those retractable leads with anything bigger than a small cat. You will get hurt with those.