Just thinking out loud here, but do they make a metal cut-off type blade that can fit on a 10" chop saw? Build a jig that will hold the drive (or 2-3 at a time) then cut them in half. Probably can do this off the back of a pickup on the customer property if drives are already removed or easy to remove quickly onsite. I would guess that it would do the trick. I also know they make a big machine that grinds hard drives into small pieces, but do they make a more economical one that would allow onsite destruction? I was thinking that during an ecycling event i could hook one up and run it every 30 min...let the kids throw them into the bin and watch it do its job. Kids (and some of us scrappers) love to see destruction in action