If you're determined to exceed the
speed limit, the best way to defeat both speed cameras and laser detectors is with a
stealth license plate cover.
The stealth cover is transparent, but deflects the signal so that a reading can't be made. License plates are usually made with a crystalline structure on the surface so that these signals will bounce back to the detector regardless of the angle, so this is the area police aim for. The stealth cover does not allow the signal to reach the license plate, so the signal does not reflect back to the camera or radar gun.
Of course if the camera or radar gun is directly behind or in front of you - you might still be SOL. The cover might also be illegal in your jurisdiction.