Scratch, Scratch, Scratch on my fence

I was out sitting on my porch last night after dark so Brownie could get her last pottie in before we went to sleep. I watched her wander around the perimeter of the yard, then she stopped in the corner and seemed to linger there for quite a while. I figured I'd better go look to see what was going on in that dark little corner. I walked up and she was wagging her tail and peering through the cracks to the other side of the fence. I put my eye to one of the cracks and I didn't see anyone, but then I heard "scratch, scratch, scratch" from the other side of the fence. I couldn't help myself. I hightailed it back inside and made Pooker go out to see what was out there. Of course, when we get out there, whatever was there is gone and Pooker was looking at me like why did he need to go out in the first place. What good is a big, strong man if not to defend his Sweetie and his Bip from the unknown?