When i carry two cameras, i hold either the video or the SLR in hand and have the Nik V clipped to my BC on a d ring on the shoulder strap. No strobes usually. But when i do have strobes on it i use Aquatica/TLC arms and make sure they are folded up nicely and that the lanyard on the clip is very short. Not good for getting close to coral...
Or i just carry one in each hand and travel close to the bottom, that way its easy to put one down and utilize the other.
With just one camera, it never leaves my hand.
However, my buddy used to shoot up his sausage for drifting safety stops and always clipped his camera to the bottom of the rope.