As part of a Mars lander, might one drill with say 1-2 cm bore probe, with a burr head; and somewhat further proximal, a laser light and associated spectroscopy, including infrared? Thus further ascertaining element/mineral content, and nature of any ice-like strata? Sub-surface apparrent ice can’t just consist of hydrated minerals, can it? The drilling could be quite slow and intermittent, with supplemental solar energy input.There would be no sampling and no casing problems.
Alternatively, might surface Martian glacier(s) be suitable? However the problem of hitting rather small target area.