Actually my LDS also has "octo keepers" that are identical to snorkel keepers but one side is a square instead of a circle. Same price, but easier to get the octo back on afterwards.
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I've heard of making a neclace out of shock cord. Does anyone have instructions on how to do that?
Those pre-made necklaces do tend to be too long.
You can do a DIY one....and size it to fit perfectly. You just need a length of surgical tube and some zip-ties.
http://www.scubaboard.com/forums/dir/277485-tying-regulator-necklace.html
2nd stage is in my mouth, the rope keeps bothering me.
I've tried this type of necklace solution, but the rope I've used floats, so, when the 2nd stage is in my mouth, the rope keeps bothering me.
I've discarded any necklace.
If the o-ring breaks, just replace it with a loop of tied 2mm bungee just like you suggested. In the meantime, use the o-ring with no concerns...Very nice work.
I'd just be afraid the o-ring would break, especially if you're going to be doing OOA drills. There doesn't look to be an easy way to replace the o-ring.
A lot of similar octopus holders (maybe the one from Divers Supply) are made with a loop of thin bungee cord, which would be much more durable. Perhaps there's a way of stiching a length of bungee cord to your set-up instead?