Aggression in chickens is many times hereditary and cannot be totally eliminated. You might be able to do something to stop it for a time, but usually they are going to come back after you at some point. I breed for temperament..........this is the only way I have found to permanently solve this mean bird problem. I have never run across a mean Orp....even while judging. Some hatchery "Orps" have been mean.
Walt
Walt