What major engineering obstacle currently restricts access to the confirmed liquid water reservoirs deep beneath the Martian surface?

The necessity of drilling through miles of overlying rock and ice, exceeding current planetary mission capabilities.

While the existence of substantial liquid water reservoirs beneath the Martian south pole is strongly supported by data, accessing these resources presents an enormous engineering hurdle. These reservoirs are located miles below the surface, necessitating the development of technology capable of drilling through vast, solid layers of rock and ice. Current planetary exploration missions are not equipped to handle such extreme drilling depths, rendering this confirmed resource practically unavailable in the near term.