Originally Posted by
Pavão
Asking from a limited experience point of view, I'm trying to think of scenarios where this would apply, the only one I can think of is a long stretch of line with no markers, where you(I would too) would want to place a directional marker so that you wouldn't have to swim for a long distance before finding the first clue of which direction is which. Losing vis, becoming disoriented and lose the line could land you in a situation like that.
What other scenarios would require an installation of marker where no other reference point is present?
It is extremely easy to knock off a double ender from a spool/primary reel, does not take much of a impossible position for it to happen.
We don't use carabiners in cave diving, but put one on a D-ring and play with it, you'll see how easy it is to knock it off of it too, just to illustrate, so, I'd believe a cloths pin can be knock off quite easy too.