But one guard can guard a lot more than $20m. A normal-size briefcase holds about $1m in $100 bills, (http://www.cockeyed.com/inside/million/million.html http:

But one guard can guard a lot more than $20m. A normal-size briefcase holds about $1m in $100 bills, (http://www.cockeyed.com/inside/million/million.html http://www.cockeyed.com/inside/million/million.html, https://www.quora.com/How-many-$100-bills-can-you-fit-in-one-of-those-metal-courier-suitcases https://www.quora.com/How-many-$100-bills-can-you-fit-in-one...), or presumably about five times that if you store in 500-euro notes. So in the end people with amounts of cash in the single- or double-digit millions would probably get together and hire one guard instead of many (you don't get rich by spending six figures a year unnecessarily) ... and we start heading back towards reinventing banks.