Lost 3 DSMB and spools? Where should I be looking on my next dive?
I don't use a BP/wing, but in my experience (rock climbing, rigging, diving) items almost never unclip themselves unless there's a semi-rigid connection (for example, a bolt-snap attached to a metal D-ring) and something to provide leverage, such as the gunnel of a boat or a tank.
I'd suggest using a small loop of thin nylon line (3 or 4mm accessory cord, tied into a 7.5cm diameter loop) and choke-hitching that to a D-ring, then clipping the DSMB to the line, not directly to the metal ring. This will probably allow enough flexibility for the clip to slide and turn on the line, without providing enough resistance to open the gate on the clip, preventing you from adding to the underwater DSMB pyramid. [Insert warnings about entanglement hazard, non-standard equipment configuration, etc, etc]