He must be yanking on that prong collar!
When I take my pack out for a walk, the last thing I want to do is to yank and drag them to where I want to go.
I like to have a relaxing and peaceful walk whereas the dogs will follow and listen to me without any conflict.
Trying to overpower them I can never win because they are more powerful than I am and weight more than me.
These dogs all came to me with a list of problems. None of them could walk nicely on leash when they first came--they were all massive pullers.
Now they walk next to me without pulling me off the sidewalk or dragging me in front of a moving vehicle simply because they have learned to relax, be calm and just follow me.
It is not because of what tool you are using (i.e. prong collar, remote collar, gentle leader...etc.), although having the right tool would certainly shorten the learning curve, loose leash heeling is all about the mindset the dogs are in when they are walking next to you.