Mouthing (adult play-biting)
Let's talk about adult mouthing. First, see your vet, because sudden mouthing in a senior dog can be pain — dogs do not bite to be mean, they bite to say stop. Step one: every time the teeth touch skin, the game ends.
Stand up, walk out of the room, no talking, no eye contact, no scolding. Step two: come back after thirty seconds. Dog mouths again, you leave again.
Step three: replace hands with a tug rope. The dog has a legal chew toy for the jaw stress. Step four: a place command before play begins.
The dog is on the mat, you say let's play, the dog gets the rope. Be the leader, be the alpha of the play, not the victim of the play. Now, the deeper fix: adult mouthing is a play-rules problem, not an aggression problem.
Teeth off skin, every time, without exception, and the dog learns what play actually means. Now here's Steve's notes.