In reply to mark s:
I've not had dogs in years now but I used to train the male gun dogs for a friend who produced and worked champions.
I think a bit of a restart is what's needed.
Retrain the dog on the lead, get it walking at heel, listening to you and to ignore everything around it (watch a lot of gun dogs walking at heel, constantly looking at their owners).
You can do this, with either a deep voice, or a high pitched voice (single word command is best).
Once you have achieved this, go to a safe environment, do it all again but with no lead. Then, start to introduce distractions but keep the dogs attention on you. Distractions can be people, plastic bags,
Cycle bells, use your imagination. Finally use other dogs as the distraction.
If the dog falters, get it back on the lead and get it back to concentrating on you.
Hope you get sorted.
Post edited at 09:31