Lowes, Home Depot, and most other hardware stores sell what is referred to as Hardware Cloth or Rat Wire. It comes in 1/4" and 1/2" weaves, and for less than 10 bucks you will have enough to cover your radiator, oil coolers, and brake ducts, intake ducts and still have enough spare material to do it all over again. Stops rocks, tire debris, and almost all but a direct hit from another car or some solid barrier.
Rap