Remember, you wrote title of this thread as "this is UNACCEPTABLE" .
That's the attitude you must carry with you. NO excuses, no mitigation, no maybe I'll ask him to stand, maybe I'll . . .
It's unacceptable for him to bite you and for this to be allowed to continue. So, with that firm thought, next time he nips at you, you EXPLODE at him. Scare the living daylights out of him. Swing the rope end hard at him , yell, jump up and down. Make him go wth? For something like 8 seconds of a blast of negative energy. He will move his feet, for sure. He'll see you in a whole new light, I guarantee it.
Remember the title of your thread!