Mat,
Old texts suggest covering the hive(s) with chicken wire - just far enough away from the woodwork,
so that the woodpecker cannot do the damage.

Questions:
1. What kind of woodpecker is it?
2. Is it attacking the hand hold area (that is if you have such things on your hive)?

Also, try putting up a bird feeder containing good quality peanuts - I suggest that the bird is
quite hungry during the cold weather!
-distraction.
Good luck - and don't kill the bird!

Peter