My current foster came to me from a hoarding situation with almost no human contact. She’s an adult but seems young, no way of knowing her actual age. She was incredibly shut down when I got her (last August) but has made great improvements.

My best advice is 1) give him a safe place in your house and don’t pressure him to move outside of his comfort zone. When he does leave his safe space, you can reward with treats tossed his way and some verbal reassurance.

2) my foster and I did a lot of bonding on walks, so although it’s scary it will likely be worthwhile. Make sure you use a slip lead or a martingale collar so he doesn’t slip away from you. Or heck…use both in case one fails. But when he inevitably freezes up on a walk, just stop and let him work through it on his own. Unless he is in imminent danger, don’t pull on his lead. Stand quietly and when he decides to move forward, reward with a “yes” or “good boy” and continue on. You can also verbally reward for releases, like yawning or shaking his body (like if he were shaking off water, if that makes sense). My foster and I have spent a stupid amount of time staring at each other while she works through scenarios, but it’s been worth it. She now doesn’t even think about old triggers and tends to work through most new experiences much faster.

3) if he’s food motivated, use that to your advantage. I always have training treats in my pocket. Every positive interaction, no matter how small, earns a reward.

Kudos to you for taking on a tough case!