On NASA's InSight Mars lander a temperature probe nicknamed "Mole" is designed to hammer itself 5 meters into the ground and measure the temperature of the martian regolith at different depths with temperature probes mounted in its cable (Science Tether).
I found this very interesting PDF on how the mole hammers itself and how temperature is acquired. There's also a video of it hammering itself into a regolith analog here on earth.
Question: How does mission control decide where to place the "Mole" module? How can they ensure that it will be able to burrow to the full 5 meter depth without hitting some sort of hard rock or bedrock?