Anyone who hikes very much in the Grand Canyon knows that rodents, squirrels, ringtails, and ravens will try their best to get a free meal from your food. Their tenacity and ingenuity is truly amazing. Once while camping at Hermit Creek, we tied a thin plastic bag to a tree branch to serve as our trash bag. That night I kept hearing a rustling noise. When I got up to inspect, I found a mouse had apparently walked out on the limb and either crawled down the thin bag loops or dropped from the limb into the trash bag, but was unable to climb back out due to the bag's slick sides. On that same trip, I set my day pack down for only a few minutes with some cashew nuts inside. When I next looked over at it, a squirrel was sitting on top of it, had ripped my pack open, and was eating my nuts. The two other times I accidentally left food in my pack overnight I awoke to find that mice had eaten through my pack to get at the food. Ravens are renown for flying into camp, picking some food item up, and flying off with it. They also will land on food bags or packs hanging from trees and tear them open to get at what's inside.
There are numerous home-made protection devices such as cookie tins. Some of these methods work better than others. For many years, the only two commercial products available were the Ursack and the Ratsack cache bag.
The Ursack is a bag made from from a high tech material called Vectran, the same stuff used in the Mars Rover landing air bags. It is virtually impervious to biting and gnawing animals. It uses a metal drawstring to close the bag, comes in one size only, 8" x 13" or 650 cubic inches, weights about 5.9 ounces, and costs $59.95.
The Ratsack is a stainless steel mesh bag that comes in three sizes:
I found the Ursack to be a little small for anything but a one or two night hike. I also did not like its closure system. I felt a mouse could crawl through the opening even after pulling the metal draw string tight.
Of these two, I personally liked the large size Ratsack. It had ample space to hold all my food, even on lengthy hikes and it rolls up nicely around my tent. The Velcro closure system is fool proof and easy to use.
Even though the Ratsack company website is still active and will accept your money, most people now indicate they never received their order, their money was never returned, and they could not get the company to return a phone call. Due to the widely reported difficulties and lack of response from the Ratsack company, that product is no longer carried by the General Store in Grand Canyon Village. Two new products have recently come forward to fill the void: the Outsak and the Foodsack. Both are similar in design to the Ratsack and utilize a mesh stainless steel bag with a Velcro closure system. The Outsak is a lighter duty version and some people report that animals were able to penetrate it. The Foodsack is the heavy duty version and appears to be bullet-proof, so it is the product that I recommend. I have and use the Foodsack.