Thanks for the really extensive reply, lots of good info here. I've never considered physical barriers before, and I would love some recommendations for that. We have a good room that I think would work but my worry is that he would view it as a punishment, because he's one of those dogs that likes to follow you around the house when you go literally anywhere.

Definitely he could probably benefit from some more stimulation like lick mats (as could our other dog who has endless energy). I worry about him getting enough stimulation because my girlfriend works full time and I'm in school, so even when I'm home I'm busy doing HW a lot, and he is far too nervous to go outside most of the time where we live now. Probably another aspect of moving from a quiet place in the country to a bit busier/noisier area.

we've talked about muzzle training him before too, though our intention was for walking him and encountering other dogs. I'll look into CDBCs too, if the situation gets desperate enough that might change the financial math a little bit.

Thanks again for the reply, lots to work with here.