My 2 year old that I've had since a pup always had a good disposition. Not aggressive towards other dogs and would listen. Just know, if he doesn't want to do something, like get off the couch or go back inside, I notice he is starting to get aggressive, growls, etc towards me. I do not give in and let his win, but don't understand this sudden change and not sure what to do. He could be like a mule to drag at times. Any suggestions?