With the 7D, I’d turn off the half-shutter press off so you are focusing on the rear button, find a suitable subject, no current or swell, and a place where you can put a sand spike to rest the housing on. Use the rear lever to focus to the magnification you want approx then release. Using the sand spike, gradually ease the housing forwards and backwards until you see the subject in focus and then pull the shutter. Take lots of shots as the DoF is very minimal especially as you increase to 1:1 on the lens. Think about the out of focus areas and how they will appear in the image. Breathe and work within depths that you are very comfortable with. Spend 30 minutes with a subject.
Just returned from a Photo workshop I was running in the Philippines. I didn’t take the 105mm macro off my D7100 for 9 days. Here are some results with the outrageously strong and sharp Nauticam SMC. Mostly uncropped.