Well, here we are, and I know somewhere, someone has thought of it but I'm putting this suggestion in.
“Buoy Marker's”.
Would be great to place (in the water) to mark and check distance's using the dioptra, combined with the marker flags we are able to create, with regular or mooring rope. This would allow measurement of deep water to perhaps calculate: dirt amounts, slope, distances more efficiently. Simple but highly needed idea. It could also be used to put on a dirt pillar for bridges, of which dirt is being added, to calculate remaining amount needed to finish.