I've been told that the use of either CS (tear-gas) or OC - pepper-spray - should not be used on truly deranged humans OR dogs. It doesn't effect either one enough to stop them - just makes them both madder. For a human that would be like someone truly psychotic, for whatever reason, or on powerful drugs like PCP. For the canine, I would guess rabies is a contender. I was approached once by a rabid dog. It was barking and growling and jumping up and down in the shallows of a local river. It was utterly on another planet! I was in a motor-boat and it started towards us. I pulled a pistol and we outran it. Called 911.