I know this thread is old. There is a new product sold at Grand Canyon. Its called "outsak" and its a rodent proof bag sold at the stores along the south rim. I was skeptical when it was recommended to me, thought it was another nickel and dime situation, wanting to squeeze me for $$$. $25 to get in the park after paying for a permit and hotel reservation. Sorry, still burns me up how much they charge to get into a park after you have already spent so much for a backpacking trip.
Done ranting. Outsak saved my food on the second night of my trip in May 2009. I was 2 days in, 4 days to go on the trip and some sort of animal attempted to get my food. The Outsak stopped them cold. I had my food inside ziplocks, inside a nylon bag, inside the outsak. There were a feew spots where animals pulled on the wires, they nibbled the nylon bag a bit, but couldn't get far enough in to get at the ziplocks. Layers of protection, i guess are the key. If they would have gotten my food, I would have had a two day walk to get out on very little chow. Even if an animal chews a corner of a bag, that meal is gone in my book, especially in Grand Canyon, with the disease these rodents carry.People have died from exposure to these diseases, and recently. At least one in 2008, and one in 2009. Not the way to end a backpacking or river trip.