This is a good topic. I was recently out with a group of friends doing a 175' dive in Lake Ontario. Boat guy (also a friend) had dropped the mooring line at the end of the season. We found the wreck on the sonar, dropped a little mushroom anchor and float, and he went down to locate the line, and shoot it up with a bag. He was diving a REVO.
All goes according to plan, and the line comes up, and we wait for him to surface. We expected him to have a little look about before he came up. After about 15 minutes, I noticed a DSMB about 100' astern. Some speculated he was at the other end of the wreck, but it was too far away and moving further away. There was a fairly thick fog, and a decent current, so he was moving away quickly. We were 12 miles offshore, in a shipping lane, so it was kinda good we noticed.
We opted to move the boat alongside and watched, and since boat guy is solid in the water, we weren't concerned. At 175' deco racks up quickly, but while we were waiting, we decided we really should have a better way to signal topside if all is well or not. We knew he wasn't on his BO since there was only the occasional bubble, and eventually he surfaced. (Seems he'd blown the bag while the anchor line was extended out from the wreck. Off it went, and suddenly he's 200' from the wreck, it's pitch back and he couldn't find it. Lesson learned.
Anyway, hence-forth, it's two SMBs if help is needed, one if all is good. We sort of all knew that, and we all had multiple bags, but best to remind everyone.
A sweet dive followed regardless....