Extremely submissive non-barking GSD

[LoveMurphy]

Our German Shepherd Murphy never, ever barks- I mean, I haven't heard him utter a single bark. He is neutered and 3 years old. We adopted him from the Humane Society. They say he was dumped by his previous owner by the roadside, but that he had been microchipped, so they were able to scan him and relocate the owner, who didn't want him back. When we got him home he followed my husband everywhere he went and went bonkers when my husband left for work. When you walk him, he keeps turning around to make sure you are still there, even reverting to the "standing hug" sometimes. I am curious if the previous owner may have abused him or just neglected him all of the time. The dog has a strange issue where he climbs everything he can- couches, fences, gates, etc. Anything he can get on top of, he does. He always sleeps on the end of our bed.

I am not complaining about the non-barking issue, but I am curious as to why a dog would not bark at all and would be so concerned when you leave the room. I am being told I should consider crate training to make him feel he has a safe place to go where he is surrounded. Does this sound like a good idea, or would it bring out the vulnerability in him more? He is a loving, cuddling, mellow dog except for the separation anxiety.

If it matters, we have one cat, who he plays with but doesn't hurt.