I built a 6X6 shooting house four years ago. No real issues until just now. The exterior walls are treated plywood. Just checked it today and the squirrels have chewed a lot of the wood, plus chewed two holes clear through it. Is there anything that I could paint or spray on it to keep those rascals at bay?
I second the porcupine theory , squirrels usually leave nutshells or some type of food behind. Like Steve said porcupines just love plywood. I helped tear a cabin down before because porcupines destroyed it.