Hello and welcome. My name is ***** ***** I have been in the dog field for 25 years. I am a Therapy Dog & AKC Evaluator/trainer/ as well as an assistance/service dog trainer, specializing in behavior. It will be my pleasure to help you today.
It sounds like a compulsion or boredom.
What type of personality does the dog have with strangers, shy, fearful, outgoing?
What type and how much activity does he get?
What type of toys do you have?
What have you tried so far?