how to stop.

If they are stepping in toward you, you have several options instead of ducking down. First, you can fire a jab as you step back, trying to keep seperation and distance inbetween you and the opponent. You could also slip, and step to the side causing your opponent to have to reset, and turn again to face you. Fighting while going backwards is something you may have to work on, as well as your footwork to help you maneuver around these situations.

This reminds me of Morgan Freeman's narration in that boxing movie he was in with Clint Eastwood which I can't quite remember right about now. He says something lke "the thing about boxing is that you have to go against your natural instincts. Everything is done in reverse. If you want to move left then you step with your right, if you want to move right you step with your left.

Was the movie Million Dollar Baby Now back to the subject, maybe you could use that to you advantage. If your right handed when you duck hit him with a left hook to the body, then quickly come up with another left hook to the head, and finish it out with a right cross to the head, if all puchs land it is very effective.