I know this might seem like a strange question.....but here goes...

Our DS9 has autism and has no concept of fear/danger. This is our first time taking him to WDW (which we are ecstatic about!) but we also have a real fear about 'losing' him in the crowd as he tends to wander/run sometimes with no idea how dangerous it can be . I already have plans in place for id tags, taking pic in am, etc. But we are seriously considering using a tether of some sort to make sure we don't get separated. He has recently started not liking to hold our hand but wants to hold our arm instead..which is fine for daily life but not in the parks. So we were thinking of something that would attach to his belt loop (he wont tolerate anything that he can see like on his wrist) and then attach to our belt loop or something to make it hands free for all of us. But I've not been successful in searching online for anything. Also, I believe we need to make the 'rope' part of it lightweight (well all of it really), and I'm not sure how long to make it. At one time we couldnt go walking on our property (we live pretty far back in the woods) without him running and I tried using one of those retractable leashes but it wasnt very friendly because it would get too long and drag, and holding it in one's hand is a strain. I can't imagine doing that for 8 days in WDW. (I know this all sounds terrible.....but you have to understand how terrified I am of losing him ). I know they have harnesses for toddlers, but they are not big enough, and he wouldnt tolerate an animal on his back anyway.
Does anyone have any experience with anything like this or any ideas for us? We are so totally excited about taking our special guy with us and showing him the world...he keeps talking about "Ditty Our World" and "Mickey Moush".....but I also want to make sure he is safe and we can do it in a way that is pleasant and comfortable for all of us. Any suggestions or experiences would be so helpful!