This DIY is designed to stop the dirt and rocks that lodge in the rear fender seam just in front of the rear tire. They are on your car, just go out and look. My main concern is that when detailing or washing the car, one drops into the cloth or wash mitt and I end up dragging a stone across my paint. It appears the problem is due to a large gap in the inner fender liner which allows debris off the tire to enter the inner fender. This is how I fixed it for $5.

I pointed it out to the plant manager when I was at Carlisle, that even a new Z06 with 400 miles had all rocks in the seam. He did not seam to care, and that Z06 was driven by Dave Hill