I did have a brilliant idea my boy told me about from one of his sub friend with the mailing back anf forth of a key to a chastity device, I thought it was brilliant. And yours is just as grand an idea. Im really loving hearing all these ideas from this message board.
A large auto parts store like pep-boys (lol) typically will have larger o-rings that are more durable (syn. rubber) that will last a long period of time. They'll usually be behind the counter though.
I wear a rubber ring on a regular basis. I have found a size that is for every day as well as sexual play. Its a lot more comfortable than steel and has no problems at airport security.