A pocket full if 5 mm baa bearings does wonders for paint windscreens and radiators
Never tried it myself but I knew a mechanic that said it worked!!!!!
One thing that does work well for those tailgaters who are simply not paying attention is to vary your speed up and down a few mph/kph...it will throw off the tailgater (wake them up) and they will usually back off. I don't advise this if the tailgater is being aggressive and yelling out the window.