First of all thank you for adopting a rescue dog
and welcome to pets.ca
I imagine the poor guy would have separation anxiety as he would be so afraid that you are going to leave him. :sad: Rescue Remedy does not work for all dogs and it didn't work for mine.
What I found to work best is to leave the house for no more than a few minutes and then come back. Do not make a big fuss over him when you do come back in....just go about your normal activities. Then leave again for a few minutes longer and keep repeating over and over increasing the amount of time you're gone.
It does take a while but it's the only thing I found that worked. You can give him a stuffed Kong to keep him occupied and hopefully his attention will focus on that.
Oh, and we would really like to see pics of your boy when you are able to post attachments.....we love pics here.