Some trainers do specific workshops/courses on loose lead so it might be worth having a look to see if anyone near you does. For e.g., I know a really good one up near Lincoln who runs a 3 weeks loose lead and recall workshop. It can sometimes help to see others struggling and tackle it together.
Otherwise, Battendog responded best to the stop/start method in which I stop like a dead weight if he pulls and don't start again until he makes the lead loose. We bagan by using treats to lure him back to my side but now he checks himself and comes to my side if he wants to move forward. It's a looong slog, though. It took him several months.
During that time we've had two set of kit:
- a flat lead and collar for the walks I want to be training type walks. These are the one where I am strict about no moving forward until the lead is loose
- harness and lead for the more fun walks where I just want to exercise him and not worry about training
The idea was that, as he learned to behave, the harness set-up would be retired and all walks would be on a lead and collar.
It's worked pretty well and while it might have slowed us down a bit, it's meant we could still have fun walks to tire him out and the different kit was an indicator to him that there were different rules.
Dogs do what works, so if they are doing soemthing then it is working for them in some way. Stop it working, make the thing you want the thing that works and they should get it.
Pulling = get to move forward and go for a walk = keep pulling
Pulling = I have to stand here tied to this log of a human = doesn't work = don't bother pulling
Worth noting that when something has worked previously and you stop it working suddenly, the dog might get worse before it gets better. This is because it used to work so he will try the old thing harder before giving up on it.