The costs for the care and maintenance of the memorial (for example, the special glass pane must be replaced every three months) are covered by Wall AG.

Huh?

[(badly) Auto-translated from citation:] But all the people who run across the square every day leave their mark on the disc. Especially in winter, the glass suffers from spreading agent. There is hardly anything left of the monument underneath the earth.

That doesn’t really explain why it should need to be replaced so often. Unless they want it in perfect condition…