That Clemente is worth as much as a nice used car. I can't imagine letting it out of my sight for even a minute.
A good idea for dealers will be to put these ultra high end cards inside a second plastic case, like they do at retail stores, either chained to the counter or with a tracking device/buzzer inside. A case that would be difficult to break without a large bolt cutter or saw. Hard to bring a tool like that to a card show.