Originally Posted by Sunflowers
I got a long walking stick. Held it horizontally, angled downward. Whenever he tried to get ahead, he would walk into the stick. Didn't like that very much, so he learned to heel.
I did something similar to teach my dogs to walk behind me. But with a shovel (hey, we get like 7 months of snow cover here).
The shovel blocked their way if they tried to nose ahead, and I first started training in shoveled walkways with a wall of snow on each side so they couldn't get around me or the shovel very easily. Just worked on it in our driveway.
Now I can be out in a field or walking on trails out in the woods and they get behind me on command - still working on the focus for them to remember to stay behind me (they get distracted and start moving around or ahead), but we don't normally walk like that. For me, it is a safety/control thing for when I want to take control on an off-leash walk.
For regular on-leash walking - I would start using a prong as others suggested. I'd also try to burn some excess energy off before a walk or a training session, so he is calmer. If you have a yard, or have access to a field, play fetch, or have a flirt-pole sessions until he is good and tired, THEN go for a walk with the goal of teaching proper heeling.