I chose to use a circular saw slightly larger than my round lights. I cut the hole so it was recessed all the way around, then chiseled out the center so it was nearly flat. The I used a Dremel with a high speed cutting blade to route out a groove from the base of the round hole down to the deck so I could recess the wire.
I am now looking for a way to hide the wire. I have thought of caulking, but may try using some copper colored aluminum flashing instead cut into a 1-inch wide strip and tacked into place. No need to paint and it should withstand the weather.