Again, a silly premise.
Thousands of years from now, either we'll have a civilization that can transmute waste into prize roses, or civilization will have fallen to a primitive state. In the latter case, a few toxic square miles of a continent are going to be the least of humanity's problems.
Markers or not, they'll learn about the "taboo zone" the same way generations before us learned not to eat whole puffer fish, go near the volcanic vent, or try to have sex with Kodiak bears.