Some thoughts:
- I've found that the best way to look around for a missing buddy is to do a "barrel roll" rather than a helicopter turn. This is quicker, and helps check the blind spots above, below, and behind you better than a horizontal scan. Hard to describe but makes sense when you try it in the water.
- Dive with the same buddy in a lot in varied conditions. Eventually you'll get in the habit of staying very close together and comfortable being elbow-to-elbow in low visibility. Don't be afraid to get cuddly! Tethering is a bad idea except for some very specific advanced scenarios, like maybe ice diving. Holding hands works well though. Might feel awkward in American culture but it's normal in others. What happens in low vis stays in low vis.
- Get good at doing a modified flutter kick so that you won't knock your buddy's reg out when you're swimming in close proximity. Dial in buoyancy and trim.
- Get in the habit of always signaling (eg. light signal or tugging buddys fin) if you plan to examine something, change direction, or stop to adjust something, even if it's only for one second. Because it WILL always take longer than you think and you WILL get separated.
- Choose one person to lead and one person to follow in a specific place. Choose a formation and stick to it as rigidly as possible. "okay you're in the lead, and I'm going to stay on your right side at all times." If it's four people, choose a square or diamond with a specific person at each corner, or a single-file line where each person has a place. Assigning strict positions is probably the most effective way to avoid separation in low viz. Makes a huge difference.
- Discuss the lost buddy procedure before each dive. It might be different depending on the dive. Eg. a wreck dive might be "meet back at the anchor line" while a shore dive might be "look around for a minute then meet on the surface" or "the person with the dive flag stays down, the other person surfaces to find the flag, meet on the bottom".
- Bright colored fluorescent gear makes a huge difference. White, yellow, or green fins are awesome. Pink/red/orange colors tend to look dull brown in our green water unless strongly fluorescent. Strobes or glow sticks only help if it's very very dark.
- Consider solo training and equipment so you're prepared in the event of a separation.
- PM me if you want to try diving an interesting local training spot with truly awful vis that's great for practicing this stuff.