I went out and dealt with the rats I found to be living in the granary, forcing them out at the point of a pitchfork, but missing every time. But at least they're gone. And I found and patched the hole. I still have some clean up to do in there, but damage control is done. The building is 8' x 8' x 6' high, topped with a 6:12 gable roof. It has a 3' x 6' chicken coop (unused just now) scabbed to the side. The whole building is sheathed, sides, top, and bottom, with plywood, except for one spot. It's a small door built into the framing of the building, from the coop into the main part of the building, and although everywhere else the sheathing is on the outside, the actual door there is on the inside of the framing. The rats had chewed a 1 1/2" hole through the 2x4 door frame. Interesting that they'd rather do that than chew through half inch plywood anywhere else. I covered the hole with some flashing and a small board. I think I'll cover the rest of the outer part of the opening soon -- with plywood.