First of all--thank you for rescuing this little guy. He's Lucky indeed to have found a home after what sounds like a difficult early start in life.

I think you have to start with housebreaking as though he were a new puppy--as though he weren't housetrained, because he isn't.

My method of house training includes crating when you leave him alone, tethering him to you at other times, and taking plenty of frequent outside trips to hopefully "catch" him doing it right so you can praise. And I assume you are not punishing him in any way for the "mistakes" he makes inside. That would only make it worse.

I also think you might have better odds at predicting when he has to poop if he ate at regular set meal times. Free feeding works great for some dogs---but maybe until you get him pooping appropriately you'd be better off with a morning meal and an evening meal. After a few days of that, I'd think you'd soom both get into a "rhythm" of when pooping will happen.

Until then, I think you're doing the right things--it'll just take some patience for him to un-learn the habit he has already established. My guess is he was punished in the past for inappropriate pooping and now is fearful of pooping in the presence of any person.

You mention putting him outside on a leash for an hour by himself. I think you'd have better luck taking him on frequent walks, where you are there with him. He's not learning anything out there by himself. And walking stimulates the bowels.

HUGE ditto.

My dogs are all pre-owned, and the three most important "rules" I have are: I take the dog outside so often in the beginning that no mistakes can even happen. No bad habits can form, and the party we have for every outdoor potty solidly reinforces it. I tether the dog to me, and we bond and learn about each other. One thing I learn is the dog's body language around peeing and pooping. I can easily get the dog outside to go and be praised and rewarded if I actually have the dog attached to me. (See "rule" number 1.) I feed at regular times. I keep a simple poop journal to give me a jump-start on getting him out (walking; as Tracy says, exercise gets peristalsis going) at the right time(s).

Oh, Tracy also called it on the biggest "rule": I do indeed treat every dog who is new to the house as if he is a completely untrained puppy. Starting at Step One is never a bad plan.

Dogs get a kind of surface preference going as to where to poop. It is possible that your dog was allowed to go inside (paper trained, maybe?) My dog was also in a kennel for quite some time and there was not much difference between the tile (inside part of the run) and concrete (outside part of the run). When she got home, pooping in the grass in the yard was the expectation - I was NOT going to have poop in the house. She had been house trained prior to the kennel but was a young puppy and probably didn't remember much.

Like Connie and Tracy mentioned, I had to treat the dog as if she had never been trained. We went outside at least hourly. I was feeding only 2 meals per day and got a sense for timing. You should have seen the pooh pooh party when she went (outside). And yes, she liked being shy and tried to find a secluded spot. I would glance away when she assumed "the position", it seemed to help. The other thing that helped was playing some fetch in the yard to get things moving...

BTW, she had one accident inside in the first week she was home from the kennel, and I had a huge tantrum!! I wasn't mad at her but at my husband for sitting at his computer and not paying attention to her while I was in the shower. It made quite an impression!