We were baby sitting a Dane for a week many years ago. We also had a 6 week old Cocker Spaniel the size of a beer can. The pup kept raising up on her hind legs and nipping at the Dane's lip. Finally, the Dane had had enough, so she opened her mouth and put it down on the pup until her nose and lower lip touched the carpet. She didn't close her mouth, but the pup was covered from neck to hip, and couldn't move.
When the Dane let her up, she went to the other room at the speed of light and never bothered the Dane again.