A "hit" is a NO-NO!!!! A dog responds to voice and feelings. Your Dad could have simply pushed him on his butt with his hand while saying some command that let's him know upstairs is not an option. Like "GO DOWNSTAIRS!" Then treat him and say "GOOD BOY!" when he gets down there. The more you talk to your dog, the more he'll pick up on your voice, inflection, ACTUAL words, and body language. Believe it or not, they figure it out (if they're smart, which I think Cooper is). I think you need to get a babygate to block the opening to the upstairs if it's such a deal with your dad...