We had a dog (dead now), that suffered from severe separation anxiety. He was an escape artist. Darn! We had him "chipped", so he always returned. He was such a problem dog. We got him from the pound and he'd been through 3 previous owners. We hung in there with him. He was about 2 years old when we got him and he stayed with us until he died about 10 years later. But it was NOT easy. He was a smaller breed dog and not a "bully breed" at all. But a real pain-in-the neck with separation anxiety. Escaped many, many times and surprised he never got killed on the road.
We had to cage him in a crate when he was younger. He broke out all his teeth on the bars, but what could we do? We put him in a room and he scratched THROUGH the door until he got out.
Things finally settled down when we moved closer to my mother's house and she was able to become our "doggie day care" while we were at work. So, from that point on, he was never alone ... never. He always had someone with him. He lived to a good old age, settled down, and turned out to be a pretty good dog, as long as we never left him alone.
That may be your only answer. ... ensure the dog is NEVER left alone, there is always someone with him.