Rocket is gorgeous!
I may be able to help you.
http://rosemarydavey.com/animal-sessions/
Did something happen to him when he was 20 months old?
Out while you were walking him?
You may not remember, but I think that may have been the trigger for Rocket to start wetting his bed when he is separated from you.
I don't charge anything for animal sessions, so you've got nothing to lose and everything to gain for Rocket.
Cheers :)