I came up with a new idea not sure anyone has tried. Basically just using some thermoplastic and forming it into a ball around the key. The stuff melts around 150 degrees F and when its made into a larger object it can take a while to actually melt all the way through. You could even take this to the next level and mold it into something that looks nice enough to display on a shelf. That way my wife would always know its there and I haven't attempted to gain access because that would destroy the object. You could even mold it around something so you couldn't just pick it up and chuck it into a pot of hot water. I even had the idea of molding it to the back of my Neosteel waist band, so there the key is literally attached to me but I cant use it without a lot of work and her knowing. Just thought I'd throw this out there.
There's a number of options on Amazon: https://www.amazon.com/s?k=thermopl...prefix=thermoplastic,aps,219&ref=nb_sb_noss_1