Hello Neil
I hope I can help you here, I trap the squirrel by threading 2 or 3 Hazel nuts onto a wire, and hang in back of the trap. In front of trap and just on doorstep put some nut shells these get mr squirrels attention and mouse dont care for them.
But for me, I need big numbers of them so I dont trap until my nut marker is eaten, I put the marker nuts onto trees through my woodland. When one is eaten I trap at base of this tree, in tunnel that is ready, he will be back soon.