I used cotter pins this year on the turnbuckles for the shrouds. Never again. What a pain in the backside. As for ringdings working themselves off: Yeah, they can. Saw it happen on one of the fine tune blocks on the mainsheet of a J35, just as we were setting out to race. For the fixed rigging you're going to want to tape, whether you use cotter pins or ringdings, because both have sharp ends that can damage your sails and catch pant legs or shins of people working the decks. The downside to ringdings is the taped finished job will be a bit bulkier, a bit uglier than taped cotter pins. The advantages are they' re much easier to get on and off and they're more-easily re-usable.