This is entirely new behavior. In the 7 months hes been here he has never growled or snapped at a person or dog until this last week.
We don't discipline our dogs by hurting them. Usually just saying BAD DOG in an angry tone will do the trick. If not then they go in the kennel. the very plain empty boring bad dog kennel with only food and water, no toys. Most times it is a 10-20 min time out.
When they are good they are rewarded with treats, pats, hugs and playtime. All of them including Mack are spoiled. Everyone has their own nap pad in the office. Mack often sleeps in the other office chair pulled up beside me.

You can tell he has been abused because of the way he reacts to certain things. He is terrified of shoes and belts. Just pick up a belt and yelps and runs to his crate. The shoe thing i found by accident when throwing all the kids shows into the front hall from my living room. He was across the room and cried out and ran. He was so scared he peed.