[ZOA NOM]

Jgordon - A license plate presents an enormous reflecting surface to a radar signal, especially due to it's perpendicular placement. On a car like a Corvette, the absence of a front plate can make a significant difference in radar reflection because of the car's low profile and plastic body. Less reflected energy = shorter distance required for detection.

I'm not sure how much difference there would be on a 911, but why help the radar gun find you?

As for sprays or covers, I don't think anything short of the radar absorbant material found on stealth military aircraft would work. If you must leave the plate on the front, I would at least angle it down as far as possible to reflect the signals toward the ground rather than straight back to the source.