This is a tough thing to try and correct. I have an Ameracaune that i added to my flock that was pecked so bad she looked like raw burger. I did all you have done and had the same results. The biggest bully's I had were 2 Wyandottes. All the others would get her occasionally, but the Wyandottes were relentless. She was getting pecked mostly below her tail. Here is what I did. I got one of the chicken aprons that was as close in in color to her. The apron only covers the back above the tail. My bird was bad below her tail. So, we cut a cuff off an old flanel shirt, and safety pinned it to the wing tips of the apron so it wrapped across her butt. Looked funny, but stopped them from re opening the flesh. I kept that on her for almost 3 weeks. When I removed it, they were curious and pecked her a few times. I got so frustrated as you are. I actually sat in the run, and when the Wyandottes pecked her I grabbed them, and started pulling her tail feathers hard to let her know how it felt. After a few times doing that they were cautious to approch the Ameracauna, but still would. I then took a very limp root about 3 ft long, and would chase the Wyandottes with it for about an hour when they went after her. My Roo watched what I was doing,(he loves me), and from then on, when ever the Wyandotte would go after Miss America, he would run them down and peck em till they stopped. He doesnt hurt them, but they now have a bald spot on their back, (no blood at all, just a bald spot), I was just a few days from relocating her, and I am blessed this solved my problem. Miss America is now laying, and hanging out with the flock. My Wyandottes are being good now for 3-4 weeks. All I can say is I feel you pain, and wish you the best, Hope you find a solution......... All the best...R