The basic problem is that the speed of a sand particle becomes an awesome abrader when the tips of the rotor are considered. Most blades have a hard metal erosion strip bonded to the blade at the last 35% of span or so, where the tip speed is worst. The strips are stainless steel or nickel.
These strips still ebrade, so the US Army uses a clear tape that covers the strips, and lasts about 20 to 50 hours, before it has to be replaced.