I also run the oil cooler below my radiator. I have some perforated 1/4" screening in front to catch tire boogers, rocks, small car debris, and grass (volunteer grass cutter sometimes).
To date I haven't caught anything from the bottom that has dented the cooler. So I would say it must have been just a coincidence that you caught something. Leave it where it is unless others have experience with damage to the cooler.
[This message has been edited by Allen Brown (edited June 10, 2003).]