There's an installation product that is a stiff piece of steel wire, maybe 20 gauge, that's used to drill down through a floor. You locate the wire under the floor and use its position as a reference. It's not a drill, just a piece of stiff steel wire with its end cut at an angle. It leaves a really tiny hole.

I've worked in a crawl space that was paved with concrete. It was way worse than dirt. If you get a rock under you, it sort of pushes in to the dirt. This crawl had a few rocks here and there, and a rock does NOT give when it's on concrete!