That Gnawing Noise

There is a persistent and annoying noise coming from near the air conditioner in my office. My initial investigations seem to implicate a squirrel that is trying to gnaw through the plastic around the AC unit in order to escape into the warmth of my office. I can sympathize a bit, as its bloody cold outside (and shouldn't the squirrel be in hibernation right now, anyway?) but I would rather NOT have a hole gnawed in the plastic. I've made several attempts to discourage him, but so far it only stops him for a few minutes at a time.