Weak? Do you mean weak-eyed? I've run cattle that aren't stopping unless something makes them stop. That something is 50 lbs of pure grit that grabs and holds. They can bark, slash, etc all they want and those cows won't stop.
*I should have specified in my original post that my experience is with cur dogs. Not trying to throw a blanket over all dogs... I've only worked with BCs on cattle a couple of times. Different style, but very handy.