I like the flexibility of clamp-on rod holders, but even when mounted tightly on a stern-mounted grab rail, I've found they can rotate and potentially damage the gelcoat on my boat. To prevent this from happening, I went to the hardware store and bought 1" diameter white, rubber chair-leg tips and a 1" dowel rod. I slipped the tip on the dowel and cut it to the same depth as the tip. I then took some double-sided foam tape, stuck it on the end of the dowel and trimmed it to the 1" diameter. Lastly, I put it in position under the rod holder and pressed it in place. In addition to preventing any damage to the gelcoat, it also holds the rod holder in a more vertical position so the rod stays put.