Every sloppy ride, there is someone who refuses to use clip-on fenders, thereby spraying their friends and frenemies alike with road slop.
I am forever hassling these riders and in some cases, I stop inviting them on rides (PVB, even though you are a prime offender, you will always be welcome on my rides).
The purpose of this post is not to complain about lack of fenders, it is to make sure that the people who I have goaded into getting them don't mar their frames when mounting clip-ons.
Clip-on fenders have little rubber stoppers where they come in contact with your frame. In theory these should prevent your frame from being scratched by the fenders. Don't be fooled. Sand and grit gets under the rubber stops and etches the clearcoat. Eventually it can wear through the paint altogether.
My advice is to wrap your seatstays and your fork in electrical tape so that the areas of contact are protected. As you can see in the photos, there are scuffs in the electrical tape where the grit would have scratched my frame.
Matt Roy has some pro looking rubber wrapped around his contact areas, but few of us will ever attain Mr. Roy’s level of professionalism.
My IF has scratches from before I knew better. I hope that I have prevented you from messing your nice frame up.