I had the same problem on my brick on both sides. The issue I had was that in rain or snow teh rugs would get soaked from crap shooting up in the wheel wells. My solution was as follows:

1) Put the car up on ramps

2) Using pliers, metal cutters, and a sander with 60 grit or less cut/sand/or snip all bad metal you can get off. Get as much of the bad metal off as possible.

3) Once you have it all out mix some hardening compound (I prefer non-fiberglass because its easier to deal with, but fiberglass is stronger), and paste the compound on from teh bottom. The rug will serve as a backboard to paste against and allow you to smear a solid layer on.

4) Apply the first layer, wait for it to dry, and apply another layer.

Problem solved for me.

good luck,
rt