A key attached to the collar?

Lately I’ve been thinking about a simple yet effective method to be tied up, with a release option, that you could use almost anywhere. And one idea I’ve come up with: if you have a leash with a ring, and a key frozen in an ice cube on a string, you can tie the string to the leash’s ring. Then, with the leash and key at the back of your neck, put your hands in front of your body in cuffs. And if you have the leash and key in front, place your hand behind your back in cuffs. But then you would still need a way to prevent your hands from reaching the cube. You probably should also be unable to move around much, since you could crush the ice between your neck and an object. Ideas?