Believe it or not, I had a backpack nearly destroyed by porcupines. It seems they are insanely ravenous for salt, so an empty backpack against a tree, with nice sweaty shoulder straps, is a primo snack.
Same problem in Glacier NP. We ended up sleeping with our leather boots inside the tent with us. Stinky, but we didn't have chewed boots the next morning. The rangers also told us to pee on a flat rock if possible, so animals don't dig up the soil trying to get to the salt. I was a little suspicious about that advice. I bet they had a big old ranger laugh after we walked out the door, and told the next group that they should pee into the wind, possible...