
It will be a logn slow process tio deal with his seperation anxiety, after all this is a habit of 9 years that has becoem ingrained and the dog is actually distressed not just acting out.
First he will need time to settle with you. It will help that if you keep all interations with him fairly cool, especially if about to leave, no goodbyes or lavish greetings.
A referal from your vet to a reputable behaviourist who could help with implementing a regime for weaning him ovf over dependence on you and increasing his confidence when alone will be needed.