I have a standard medium size boltsnap (1" eye for finger) tied to the bottom right hand grip on my Aquatica using 5mm prussik cord. once tighted correctly and the sail water hits it a few times, the knots becomes bombproof.
To go hands free for a short period I'll typically chest clip the rig off, but for longer hauls (e.g. scootering or laying line) I'll wrap it up and clip to my right hip or wing d-ring. I don't like the idea of a long tether because it is an entrapment concern, though I'll admit this is mostly a tec thing.
I'd also recommend against using keyring (aka splitrings) as they tend to catastrophically failed under load and it doesn't take much for that to happen. Might not be a problem in the water, but I could imagine a tossing boat and handling issues becoming a problem.
I like the Cetacea lanyards. I use those even on my dive lights, in addition to the camera.