My partner and I have 2 dogs. A 10 year old Pit Bull (Eryn) and a 1 year old runt mix (Baloo). We adopted Baloo when he was a few weeks old back at our old house in Yuma Arizona. We potty trained him just fine, we had a dog door. After having him for about 10 months we had problems and had to move back home to Fort Mohave, Arizona and in with his parents who have 3 dogs. We stayed there for 8 months. There were no issues. They have a dog door. They would also from time to time leave the dogs outside and let them play, locking the dog door due to small children. Baloo didn't like that. He'd whine constantly, but still no accidents.
After 8 months there we finally bought a new house and moved in. It has nice wood flooring (thank god), but no dog door, and sadly money has been too tight to buy one. The first few months Baloo did fine going to the bathroom with his sister Eryn. Then all of a sudden he started going inside, but not all the time. He'd go outside too. We thought oh maybe we were just away for too long. After a while he refused to even go outside. He'll stand by the door like he normally does, but when we open it he'll back up and just stare outside. We'd get Eryn to go outside since sometimes he follows. Sometimes it works. It hasn't been working more and more. He refuses to go outside. Granted we live in Arizona and our summer this year has been up to 127 degrees. The rocks are hot. I get that. But he stopped going outside at night time or even when the past few days it's been 80-90 due to aftermath of rainstorms. Baloo still refuses to go outside and it has come to a point where anytime we leave the house and return or go to bed he poops inside. When we come home/get up. There's poop in the entryway of the house. Sometimes even pee.
I"m at my whits end here, but I will not give Baloo up. We did just start trying to do reinforcement training, giving him a tree when he goes potty outside. But it is way to early to tell.
The dog has had a lot of change in his life. I think you are doing all the right things and he will be retrained in time. For now, make sure you clean up his messes with a product like Nature's Remedy. It will remove the scent so he won't go back to the spot. He may have to be crated.
I think your dog is traumatized now. If he was left in the yard and the dog door was locked, he is now afraid to go outside to the toilet. What you might need to do is put him on his leash before opening the door. Take him for a walk around the backyard and let him go to the toilet. Afterwards, praise him and bring him back in the house. Your dog is afraid you will lock him outside and therefore he doesn't want to go outside to the toilet.
First off don't discourage your dog and start going outside with your dog and do this for a lil while and when your dog decides to pee reward her with a treat! Most of the time dogs love the taste of chicken so try that and see if it helps!