You can take a black zip tie and a piece of 1/16 inch bungee or nylon cord of appropriate length, put it under the zip tie around the lens barrel and put a knot in the end and burn the knot closed, tie the other end to your tray or housing or clip it.
I lost my Inon UFL165AD off WPB for three days and another group of divers with the same operator found and returned my lens to me, unharmed!!!!!!!!!! Yep, it came off in a rough entry! Actually, I think the operator purposely put a group of divers on the spot to try and find it (drift diving so hard to pinpoint the exact spot), anyways, they found my lens and gave it back to me.
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