It's happened numerous times to me, and i'm sure it's happened to you.
Let's say you're the captain, and you sustain some damage that's not-so-easily fixable. So, your solution.
Send an engineer out with a diving suit to assess and repair the damage.
A few minutes later, he radios in the damage, and reports that it's been repaired.
You check sonar, and it doesn't look like he's outside the ship anymore, though he never did check in.
Well, you're losing time so you go ahead and get a move on, but not long after receive a panicked transmission from the engineer saying that you've left him behind.
So, now you have to go back for him, wasting even more of your time.

I propose an the all new, arcane technology of the CABLE TETHER!
Something that could hook up to the door or some place, or maybe even a special 'hook' item. I say door because it'd make it easily implementable with older ships that are no longer being kept up to date.
You could hook the tether up to the solid object, then to your suit, so when you slipped outside for a water walk, if the ship were to start moving, you wouldn't be left behind, giving you ample time to radio in that they need to stop.
Or, if you're the captain, this could save your bacon from leaving an innocent crewman behind because you didn't realize he was still outside.