One of my dogs, Sasha, (aka Boogie) is one of those dogs that cannot be fixed, so like you, we manage her.
I took her to a class that was specifically for crazy dogs - as a courtesy to the less crazy dogs in the class, we left. The instructor is a friend of mine and he said she is one of the most messed up dogs he has ever encountered.
She is a product of poor breeding and she lived the first year and a half of her life in a dark garage. She lived in there, slept in there, ate in there and relieved herself in that same dark garage. She did not have interaction with either dogs or people.
We have successfully rehabbed hundreds of dogs over the last 20 years - Boogie cannot be "fixed". Some of the dogs we "fixed" were pretty bad cases that took a lot of time and patience before they were adoptable. Since Sasha never became what you would consider adoptable, we adopted her ourselves. We keep her safe and do not allow her to make any bad decisions. We walk her in areas where we do not encounter lots of other dogs or people. For the most part, she is pretty good with all of our foster dogs. She growls a lot, but things rarely progress beyond her growling. She is ours and we love her, but she will never be a normal dog.
Please don't think that you have failed your dog.
Yours in GSDs and rescue,
Good Dogs for Good Homes
Virginia German Shepherd Rescue