WOW! What the f&*%, over? I have seen "rings" at a few marinas before, however they were definitely better attached to the dock better than four little screws. And, I don't think I'd trust my boat to some marina's dock-line that had been there for God knows how long. The good news is that marina must not see any winds or current if the system has lasted long enough for the ring to rust. I think if I was docked there, I'd have a pretty good collection of rusted rings with dock-lines attached in no time at all.
This past weekend, I successfully pulled out one of the marina's dock cleats. I'd returned to my slip and was running my 20hp inboard diesel to blow the silt out since it was low tide. Suddenly, my boat shifted slightly and the spring line went slack. The cleat and the 2X6 it was attached to were dangling from the end of the line. The beam supporting the 2X6 had rotted the two inches the cleat's lag screws had penetrated. So, I'm not sure which is worse...an old dock-line with rusted ring which is attached by four little screws, or a cleat that looks good on the surface but is really only attached by two lag screws that penetrate two inches into rotting wood? Just a thought...