Long Scrotum Lengths Keep Ring from Staying Put

Hello! My Miss and I have been playing around with chastity for some time, yet every gadget we’ve tested yields the same outcome - I still manage to get erect. This happens because my scrotum stretches just as much as my penis when it’s hard—at about 6.5 inches—so the cock ring slides along the shaft alongside my balls during an erection. In fact, I’ve slipped out of a couple of devices while sleeping because of this! We really want me to be locked in tightly and securely, but it’s been tricky. From what we can tell, a chastity belt is likely the answer, though they cost quite a bit. Also, my job requires me to spend plenty of time on my knees with my backside exposed like a construction worker, so visibility could be an issue. Does anyone have suggestions for how I can finally get properly locked up?