The gaurds off a cat can be cut off the cat and welded on the O/R pipe and when the cops look under they will think they are cats. Someone on here did this an posted some pics and it will fool most people.
it doesn't get any more real than the ones that should be on your car (gaurds I mean). I helped my friend cut his cats open and run the exhaust pipe right through them but I think the Gaurds would be way easier and look just as real when looking under the car.