I have to install an outdoor shower for a rinse off to the pool. The shower
valve has a solid brass body and I have to cut a hole about 7" in diameter
to recess the valve into it.

How can I cut a 7" diameter for this? The trim is not much bigger so a
clean cut would be necessary. My thinking is that I draw the outline on the
concrete wall, then drill holes (many holes) along the perimeter using a
hammer drill. Any other ideas greatly appreciated.

MC