My late dog, a rescue greyhound, was a big chucklehead with low impulse control. The first few walks with him on the lead were a nightmare. What worked was turning the leash into a brake. If he pulled on it, I stopped. When he stopped pulling, I carried on. It took about a fortnight of twice-daily walks for him to understand (he was really not very bright), but in the end it clicked. He became the master of putting the most exquisitely gentle pressure on the leash to try and hurry me along without turning on the “brakes”.