Yes indeed John, that is a problem that many of us share. Yours is a clever solution John. It brings back memories of my childhood spent every Saturday morning in the New Haven (Connecticut) YMCA swimming pool, back in the day, naked of course. My dad would take me there religiously as a young child so that I could improve both my swimming and social skills. When we signed into the locker room, we would each be issued a locker key for the day which had an elastic ring attached for the purpose of wearing the key as we went about our workout. So the pool was soon populated with many naked enthusiast bodies, all sporting red colored bands with keys attached around their biceps.
More recently, but still long ago when I started wild swimming and kayaking in out of the way places, I adopted the habit of hiding my car key in some crevice in the external bodywork of my car. There are numerous obscure places on my car that work well. I haven't lost my car yet to this practice over several decades, and more importantly I have not lost my car keys at the bottom of a swirl hole in some class three rapids.
-Dan