Hi,
Not sure if you've tried the following things but they might be worth trying as they worked for us:
-Leaving the radio on- our dog loves classical music
- leaving him with a kong or puzzle toy to keep him occupied when you leave
- is he crated? We never crated our dog but always kept him in the kitchen with the door closed- if we kept the door open he appeared really anxious and would cry when we left.i think the smaller special space makes him feel secure.
- cardboard boxes filled with kibble- you'll come home to a mess but it's a fab stress buster and occupier.
- a familiar scent- your old t-shirt or something for him to snuggle with so he has a familiar smell.
- making sure goodbyes arnt stimulating.. We don't really say goodbye to Leo. We just ask him to go to bed and chuck a treat his way when we leave.
Hope this helps a bit