OK, again your problem is the fact that the dog is not seeing you as a permenant bond. In one way you are trying to do too much at a time and in another this lack of respect needs addressing. I am also an ex guide dog trainer and I'd like to know what your friend has to say about harness work. If a dog can not tell the difference between the lead and the long line how can he tell between the lead and the harness?
I have trained many, many dogs starting with the long line and the only problem is in the first instance as they think they are still on the lead - teaching the dog the command,"Off you go!" or "That's enough!" is enough. The weight of the connection is also an indicator to the dog. The first time a potential guide dog has the harness on he hasn't a clue what it is or what it means. This has to be taught, as long line training has to be taught, although it it should only be seen as a stepping stone to an obedient off lead dog.
Work on building a relationship with the dog before expecting the dog to trust and obey. The key to this is practice. If you rely on the dog to obey a command in the house, move this one command to the garden, then on to open spaces on the line. Never ask the dog to something you are not 100% sure he will obey until you can get the dogs attention whatever else is going on.