The problems stem from Jasper reacting increasingly aggressively to feeling trapped or restrained in any way. If anyone corners or restrains him, he may now growl or snap. Even being on lead makes him feel trapped.
His behaviour took a dramatic turn for the worse after he had been left with a dog sitter for a week a couple of years ago. One can fairly safely guess that this person used ‘dominant’, punishment-based methods on him in order to force him to comply.
He has them up and down opening the garden door, and then may decide he doesn’t want to go out anyway. He takes them his food bowl when he wants food, and obediently they fill it. Whenever he brings them a toy, they will always play. When he wants to be fussed or touched, they always oblige.