get a dashcam. Mine cost 16 GBP but there is one at about 45 that has two cameras in one device, one pointing forwards and one points backwards to the rear window. Then Put a sticker in the back window saying something like "the video of you breaking the law is now on the internet. The police can view it any time"
Sort of "if you can read this - you are too close" with a bit more byte (sic).

My fantasy is to devise a peashooter type tube that will fire stink bombs at the guy's radiator and air vents. & don't think I won't make one!

PS I have only had one useful video clip from it, and not an accident. Just a load of fire engines near the canal that tells a story. I video canal restoration.
PPS it does make you observe the speed limits a lot more closely.