I am so sorry to hear this.

I'm glad there are no serious injuries, but it's still awful that their had to be such a bad fight.
Would a behaviorist be able to help you at all? Maybe he or she could see Brock and asses him for you. I would try to pull out all the stops first, but if it is rehoming him that you have to do, I know how hard it will be, but you are doing the unselfish thing for both dogs.