Having tried everything I could to stop one hen pecking, (sprays, beak bits...) I resorted to clipping her beak.
Use human nail clippers, take off only 1/4" if that, from only the top mandible. It prevents the 'tweezer' effect and stopped the problem overnight.
It doesn't stop them eating layers pellets etc but might make them less effective finding food free range. The beak grows back - sometimes once is enough to break the habit, sometimes it needs repeating.
Incidentally, having done both, I think the beak trimming was much less painful and traumatic than the beak bits, which clip into the nostrils - ouch!