I'm trying to dismantle one of those outdoor swings - like a wooden sofa suspended on chains from a wooden framework with A shaped supports at either end.

The bits of timber are attached with what I think are called coach bolts - a domed head with a square bit underneath.

The problem is that the bolts are recessed down a hole. I can turn the nut with a socket set but because it's a all a bit rusty and seized up the head of the bolt turns as well and I can't get hold of it to stop it because the head is domed and down a hole.

Any ideas how I can get hold of the head to stop it turning?