I spent a year working on this with a friend and her Flatcoat (one hour most weeks with a few breaks for holidays). Started in the middle of nowhere with just me at a distance (dog on lead), owner feeding dog, me gradually getting closer and if I got too close and he jumped up I turned and walked away without saying anything. the owner also said nothing as this dog had been finding exclamations of any sort rewarding, even if they were 'telling him off'. Gradually worked up to me being able to run past and stroke him. Then I roped in my son to act as stooge and basically repeated it all again. Then we moved to increasingly busy areas. The key things were food from his owner and being ignored by everyone else (my role was to step in and prevent people from trying to touch him). He can now walk around a town without any jumping up - and his owner says the behaviour has transferred to off lead walks on the Downs, that he has ignored a runner and a horse rider recently. I think we built up value in the owner as I also encouraged her to play with him. The dog was four years old when we started. During the year he continued to have off lead walks with his owners so did still practise the unwanted behaviour sometimes which may be why it took so long. But it can work if you are determined and plan to set up training scenarios.
