I had a rescue greyhound, an ex-racer, and how I leash-trained him was to transform the leash into a brake. When he pulled on the leash, I stopped. When he stopped pulling, we carried on. At first we stopped every few paces, it was agonising. But eventually (he was not very bright) the penny dropped and he realised he was controlling the brake. All he had to do was walk at a steady pace without pulling and we would get to the park quicker. It was funny seeing him try to hurry me along by exerting the most exquisitely tiny bit of pressure on the lead.