Does your dog weigh more than half as much as you do, and he thinks going for a drag is fun? Here are some tips for getting that under control. My dogs have always been big, so I know what I'm talking about. Crom and Link provided some challenges that I solved with some simple strategies. They will work for you while you look for long-term solutions.
Crom was a gentleman, but unfortunately he was also a male chauvinist pig who played by guy rules. He wanted to walk 10% faster than whatever pace I set. Gotta be in front, y'know? If I ran, he ran faster. Drag at any speed. However, if I gave the lead to my wife, he would slow down immediately. How polite! We discovered this by accident, and some testing revealed that it was almost amusingly consistent. I would hand the leash to her, he'd slow down. If she snuck the lead back to me, somehow he knew and speeded up. Vibes? So when we walked together, she always held the leash.
Crom's style was inborn, from the day his puppitude arrived at ten weeks. Link was two, and set in his ways, when I got him. After three years he still struggles ahead, dragging me as hard as he can stand. Even a walking choke doesn't help. Gasping, choking, he forges ahead. I dealt with that annoyance with some adjustments to my leading technique.
First and foremost, consider getting a Gentle Leader. These ingenious devices are horse halters for dogs. Imagine trying to lead a horse with nothing but a collar around his neck, and you will see at once how brilliant this device is. Gentle Leaders take some getting used to. Most dogs hate them at first, so accustom the dog to the experience by having them wear it around the house and get treats for their trouble. Link hated his so much that all I had to do was put it on him, and without even going for a walk, he got the picture. He would behave without it for a few days after!
If the Gentle Leader is too much trouble, try a few tricks to make your own situation less precarious. First, consider why being pulled by a dog is dangerous. You are attached at the shoulder, so his momentum risks toppling you over. It's a lot easier to pull down a tree from the top than from the middle. You can lower the pull point with two tricks.
1. Use both hands. You wouldn't lead a horse with one hand if he was unruly. Use a long lead (an extra two or three feet) and hold the leash with your off hand while your main control is your stronger hand. Your control is immediately stabilized. I generally hold the leash with the middle two fingers of my right hand; that way, my hand will clutch if he bolts, but I'm not attached to him in case of serious emergencies.
2. Grasp your belt with your thumb. You've seen people with dog leads attached to their belts. You could try that, though I find that with a dog who needs control, it's more trouble than help. It isn't just to free up their hands, though. When the dog's weight is hitting you at belt level, it's below your center of gravity. Big help. I hook my thumb in my belt (or a jeans pocket, if I'm wearing durable pants) when Link gets "pully." When I get yanked forward, I'm pulled from the hip. Iit's not knocking me off balance as well, and he has to move more weight to go forward.
With Crom, the solution was much simpler and a bit of fun. The real problem is generally not that the dog is in a hurry, but that he wants to walk in spurts and starts rather than with the steady pace you prefer. I'm sure this would work even with an incorrigible like Link, but I haven't tried it yet. It's better for park walks, and we generally just scout the neighborhood. I bought a horse lead for Crom — twenty feet of nylon. As we walked, I would play out and coil back the length to keep a good slack on the line. Crom would surge forward for a few yards, then stop to investigate a good smell. The effect was similar to the automatically extending leads, which are also an excellent solution, but they aren't usually strong enough to control a hundred-pound dog.
A bit of training would solve the problem with Link, so I don't ask for sympathy. My solutions are lazier, but serviceable. Remember, if it's his walk, he should have some control over it, as long as he's polite.