He is a puppy mill dog, and was not properly socialized as a puppy. So he has two strikes against him. I have never seen him play with another dog!
I had no idea how hard it would be to get him more comfortable around other dogs, now I am thinking that perhaps it is impossible. It is such a shame, because he has boundless energy, and I feel like he would be so much more relaxed and have a better life if he could run around with another dog. But of course, when he's not relaxed, he's edgy and more vigiliant around big scary dogs... kind of a vicious cycle.
It's just such a bummer, I had been hearing how great he was doing for the past few months, and then suddenly I get a call saying, "he can't come here anymore."
The manager just emailed me a vet rec and trainer, so at least I have somewhere to start. Maybe this will be the change he needs. I have been meaning to work with a trainer for a long time, so there's a silver lining.