My solution is a long shot. I have a cat that became aggressive with my dominant male. Even though he is operated on sometimes he just feels sexy. She decided she had enough of him and wants to exterminate him. He is too fat to really mate with her but his constant harassment has her at her wits end. I usually scold him whenever he starts to chase her a bit and it stops but her retaliatory attacks got very loud with lots of howling. One day I realized that when she is wearing a harness she feels handicapped. She would walk low to the ground and by coincidence would not attack him. It's a simple harness to walk a cat that goes around the neck and chest. If she starts facing him and hissing I put the harness on her and it's over. After wearing the harness a few hours the idea passes and she is back to her usual self. I first used a little sweater I had for her this worked also. It's worth a try but I think I was really lucky she feels this way about a regular harness. It may be that she thinks he would have an unfair advantage and grab her harness in a fight, whatever reason it works for her. I hope you can find some creative solution for your problem, good luck.
Below is an image taken minutes after a fight broke out. I pick her up as soon as the hissing starts. Since I bought a beautiful pink harness which works just a well.
