I'm sorry you're going through this, but commend you for taking action and working with a vet to get him help. It is going to take time for any anxiety medication to 'on board' and reach its peak effectiveness, and sometimes it takes some tweaking of dosage and type of medication before you find what works best, so patience is definitely key! It may help to journal about his behaviors so you can look back and identify small improvements more easily, if you're the journaling type.
I strongly suggest you have a read through another thread on here, Medicating Molly, about a border collie in a similar age range to yours when she was started on Fluoxetine (several years ago now). The member is no longer very active here, but does occasionally come back to update or respond to that thread, so you can get an idea of how things worked for her and the kind of progress she had. I say 'had' because she was successfully weaned off medication last year, and seems to be doing well! Some dogs do need medicating their whole lives, and it's worth it if it provides them good quality of life, but being medicated also helps dogs learn coping skills and helps them understand that the world is less scary/threatening than they thought, especially if you actively work with them on behavior modification around their anxiety triggers, once they're medicated and can handle it.
Wishing you lots of luck - and you're definitely not alone!
I strongly suggest you have a read through another thread on here, Medicating Molly, about a border collie in a similar age range to yours when she was started on Fluoxetine (several years ago now). The member is no longer very active here, but does occasionally come back to update or respond to that thread, so you can get an idea of how things worked for her and the kind of progress she had. I say 'had' because she was successfully weaned off medication last year, and seems to be doing well! Some dogs do need medicating their whole lives, and it's worth it if it provides them good quality of life, but being medicated also helps dogs learn coping skills and helps them understand that the world is less scary/threatening than they thought, especially if you actively work with them on behavior modification around their anxiety triggers, once they're medicated and can handle it.
Wishing you lots of luck - and you're definitely not alone!