I own many radar guns and I have $1000 that none of you can beat them with a radar detector/brake hard technique. I can get a reading locked as fast as I pull and release the trigger. You will still be on the gas pedal thinking "was that another false alarm?".
Radar detectors are for fools. If you speed, you need to be very alert and continuously look for speed traps (when you crest a hill, around a bend, under a bridge, up that on-ramp you are passing).
There is not a radar jammer on the market that works. I have tested the absolute garbage produced under the various scam-artist making phazer, spirit, stealth, etc. They do not transmit anything, they passivly relflect (antenna in, wire, antenna out) and cannot even jam a person walking holding the unit with a battery. I tested these at the Chrysler Proving Grounds with Car and Driver. They are a fraud. Throw it out the window and buy a Valentine One if you need to detect.
An active jammer is absolutly illegal in all states. I used to design and manufacture them, but the FCC was not too pleased.
As far as radar profiles go, fiberglass is absolutly transparent to radar and radio for that matter. A cop will have a much harder time locking a speedster over most cars. The problem is modern radar guns used at close range won't care, there is enough reflection off of the driver to give a signal at 200'. The best defense is know the case law. You must be alone, in-front and nearest the police vehicle for the radar reading to count. If you were in a group, next to a car/truck or followed closely, you can beat it. They know the case law and I have beaten three tickets by just addressing the issue with the officer right at the time of issue. Say something like "did you get me while I was passing the truck?" and if he says "yes", you say "well at what point then was I alone, in-front and nearest your vehicle?"