Mexico (and many other MORE-ADVANCED COUNTRIES -- or at least countries SERIOUS about trying to end illegal activities by the CIA and their Republican Party/Fox News allies), REGULARLY changes the design of bills and OLD bills must be exchanged for new ones within a limited period of time -- OR BECOME WORTHLESS!!!
If the United States pulled this move and required exchanges of over a certain amount ($1,000.00???) to REGISTER with the Government with explanation -- reasons for holding so much and other details documented if any INDIVIDUAL (corporations would NOT be counted as "individual citizens" for this purpose), traded more than $10,000.00 -- those ILLEGALLY hoarding cash in US bills would have their trusted minions transport the bills to less-suspicious places than they are generally held to be exchanged, and the GREAT HOARDED CACHES would be broken up and exchanged in amounts LESS than $10,000.00.
Or they would BUY gold, diamonds, and other precious commodities as MORE ANONYMOUS ways to hoard ill-gotten wealth -- playing havoc with THOSE markets in ways that could be watched carefully.
This HUGE movement of cash and separation into MANY smaller lots would be noticed and tracked to at least SOME degree, and SOME of those foot-soldiers who actually make the exchanges for Mob Bosses, would slip up and give away info to authorities. Panic would ensue if it were handled correctly.
And then Wilmington would SUDDENLY not be so flush with cash.
Repeat every five or so years on ALL currency $5.00 and above.
BUT REPUBLICANS WOULD NEVER ALLOW IT!!!