Amen.. I use a small shoe makers brass hammer with finely radiused edges for doing below waterline soundings. Above deck I use a phenolic hammer, or brass one side / plastic other side so as not to damage cosmetic gelcoat or LPU paints... Once you find a hammer you like you stick with it....Surveyors use a hard plastic hammer. A metal hammer may damage the gel coat. A rubber mallet is too soft. Surveyors are picky about their hammers and each one is a personal choice. I use the handle of a screw driver as I can tap rapidly with it finding smaller voids.
That said a moisture meter can be used to identify areas that need more sounding, if you know how to use one, and can also track changes/migration in core moisture over time....