Well hopefully this will be Mister's last home. I think he is challenging you... trying to see if you are going to get rid of him aswell. Have you tried obedience? Some pups are very strong willed and maybe he would benefit from some professional help. He probably needs a lot of structure and needs to know that YOU are in charge. It can be hard to become alpha dog (it's taken me a while
).. you should try reading Caesar Milan's book Becoming the Pack leader. It's great and it sounds like it is something that Mister needs! good luck. hang in there.. it's hard being his 3rd home... he is confused and doesn't know where he stands in the scheme of things.