I have heard of people using this with pretty good results.
Farnam Comfort Zone with D.A.P. Spray for Dogs - Health Care - Dog - PetSmart I think you can also get collars with DAP.
Hopefully it is safe to use.
When Daisy seems stressed I put a little outfit on her that is snug. It makes her feel more secure and calm.
I hope you can find an answer. Please let us know if you find something that works.
Did this behavior just start? Maybe there is a change in his environment that has made him nervous and afraid.