Adjust the martingale every time you go out. Give him only 12 - 16 inches of leash. Walk with purpose and rather quickly. You're out for a walk, not a sniff. Keep moving. I've heard someone else on this forum say that they walk with a clicker in their leashless hand. Click when something gets his attention for longer than you'd like. You can do this. He'll soon understand that when he's attached to a leash, he's not dashing anywhere. My girl figured this out in 3 walks. They were 3 difficult walks, in all honesty, with pulling and tugging - but she got the picture. You can make him a great leash walker. What an amazing gift to give him. Good luck.