Maybe add a small perpendicular fin / tab to each fin to help it catch some air and open due to air flow?Inserting myself into the conversation briefly , I've entertained a few alternatives, but haven't found anything I thought would really work. I bought a box of all-metal thumb tacks. It might work, but they are a much smaller diameter so they'd be very loose. Oh, I should add that I'm clinging to the idea that I can launch it with the fins up and the acceleration would drop them down.