CD's/DVD's are often suggested (hanging from lines stretched over the tops of runs) as a method of deterring daytime raptors. This is a simple method of realizing the reflective potential of the disks (scare hawks/signal rescue aircraft) while rendering them nearly invisible to all but the intended targets. I posted the first shot in another hawk thread, but failed to illustrate it in actual use (the line in the pic would need to be pulled taut to maximize effect). The purple caps are from water jugs (anything flat/waterproof/easy to punch holes through will work), a toothpick, etc., (sorry, Linux aficionados, plumb-out of AOL CD's). This is just an example to improvise from. Main goal is to get the CD pulled up tightly to the line so that it remains horizontal (don't have to see it hanging there at all). And, on any little breeze, on any sunny day, you'll be producing a `disco' light show to flummox the hawks and blind all other spies in the sky.