Nothing that I know of, rats and mice can be pritty persistant. I remember that tea chests used to have thin strips of metal folded around their edges and tacked or stapled into place, presumably this was to stop rats gnawing their way in during long sea voyages. So depending on how big a job you are faced with, thin sheet metal strips bent round the edges of what is being gnawed and then tacked down may help. If its only a small job you could cut up a cola can with some tin snips and attach it with a box of tin tacks, otherwise maybe the angle iron from a bedframe or some of that stuff from industrial shelving units possibly?
