I consider small critters to be one of the "elements" so I suspend my pack from a tree branch if possible. No personal experience but I've read stories of empty packs being gnawed on just for the salt. If rain is expected I cover it with my poncho, taking care to secure it against the wind.

Or......if I'm using my Vapor Trail the pack becomes part of my sleep system. It goes under my legs and a 3/4 length pad does the rest of the job.