I use one of these to hold my deco reg up next to the 1st stage/valve. I think it cost something like $1.50 at my LDS. I bought it when I very first started diving. My g/f used the same thing to hold her octo. I went long hose/bungee necklace literally between finishing OW and my first "real" dive, so I never used mine until I went tech.
This type has been completely reliable for me, for what I've used it for and seen it used for.
It seems to me that a diver for whom this octo holder does not work reliably may need to consider why that is. Imagine a diver in horizontal trim, hands together in front of them, only using their fins for propulsion. What possible reasons could cause an octo to become dislodged from that holder? I simply do not believe that the octo would ever just fall out on its own. Something must be hitting the reg or pulling the octo's hose. Instead of looking for a "better" holder, maybe the solution is to "fix" whatever is knocking the reg out or pulling the hose. It might be as simple as rotating the holder around the mouthpiece, so it is coming off the reg in a different direction. Or attaching the octo holder to a different spot on the harness.
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