Woodpecker proof nest-box

 A woodpecker attacked the far nest-box a couple of years ago: please see http://sussexrambler.blogspot.co.uk/2011/05/great-spotted-woodpecker-attacking-blue.html for the gruesome attack.  The box was patched up with bits of old tile but has not been reused since.
An additional box was made from stouter timber and "armour-plated" with roof tiles.
No woodpecker will get in there now.  The Great tit pair busily feeding their young inside are all safe this year: of that I'm sure.  The entrance gap is tiny.  I was concerned that it was too narrow but not so it seems.

Update on 18th May 2016.
Both parents are busy feeding an increasingly noisy brood inside the box.  I imagine that the fledglings will have the strength and ability to leave the box any day soon. "Amour-plating" a homemade wooden box with clay roof tiles has worked well and done its job so far.