I know that I am falling for this engagement farming. Here is a reference to show why this won't work.
There is a very interesting reason hiding money isn't easy anymore. Many Central Banks across the world use inks that are extremely mildly radioactive.
As in they would barely register above background radiation even in a few bundles. But when there are massive amounts of notes, like this, a geiger counter will spike, not by much, but slightly above background. So even if you hide notes behind a cement wall, they'll give their location away.