Homemade Retainer Ring?

Hey all. I was fortunate enough to be able to try a Lori 2a with retainer ring. One of my friends has one. The whole retainer design worked 100% as intended. You absolutely can NOT pull out with this device. I currently have bird cage from MM and I'm just trying to think of some ways to come up with a retainer ring idea. I thought I read some where at one time someone came up with a ring and a rubber band to hold it in place or something like that. Just wondering if anyone has thought of an idea or a way to install a retainer ring. This is the next best option for someone who doesnt want a PA or full belt to prevent pull outs. The retainer ring also helps with the device sliding down when you get sweaty and your balls sag if youre outside working in the heat or working out.. etc. I'm REALLY surprised no other company has starting making devices with retainer rings.
Thanks in advance!