I think you will find anyone who has taken a dog back after rehoming it to someone else will tell you they immediately revert to considering their original home as their territory. Its only if they go to a new home with a dog already in place that they either have to defer to that dog or make a bid for 'top dog' by intimidating the resident dog, i.e. by scent marking or by pushing their way in for food, treats, attention, etc. Some dogs just aren't 'top dog' material and will allow any new dog to take over.