The idea is not to kill your models...not after I spent so much time training them in which way to point the strobe.
There are a few options for placement of model strobes. For backmount divers, between the tanks is ideal and easy as long as the cave roof is not too low. Strobes can also be placed on the back of sidemount divers on the harness (no solid backplate, I use an Armadillo, others use a Nomad, Razor or a homemade setup) but sidemounters tend to object to this. It also stops them/you travelling through smaller areas on the way to take photos. Backmounted strobes are limiting in the kind of shots you can take. Most strobes will be triggered by a flash at their face, so you can't take pictures from behind the modelling diver because it sets the strobe off straight into the camera.
So, if not backmounted, then where? Handheld is great and gives the best flexibility. The drawbacks are that your model can point the light anywhere, including at you, and completely destroy the picture. Training required! As you pointed out above, it also takes up one hand. I'm currently designing a goodman-handle type device for my z240s that will allow them to be mounted on the opposite hand to the primary light. This will hopefully let photo models do things like put in line without having to clip off the strobe. Clipped off strobes usually end up pointing the wrong direction...
I sometimes tape the sensor to the back of the strobe, which reduces the amount of fiddling for the model but means the strobe must be visible in every shot to fire - no magical hidden lights. If I can get my hands on some longer cables, I intend to experiment with running the cable from the strobe hand to the sensor hand by going up each arm and across the shoulders (under the harness). The sensor will then be held with (and possibly attached to) the primary light lighthead. The triggerfish don't seem to have any problems with being right next to a steady light source.
We'll also be carrying shears that will cut the cable, but with it flat to the body it would be a struggle to entangle in anything. I also doubt this would be a setup I would use where there were nasty restrictions or a chance of tank removal being required. As usual, both strobe and sensor can be clipped off out of the way by the model. If it all goes pear shaped, all the camera gear and anything else superfluous to requirements is staying in the cave until I feel like coming back to get it.
Safety first...but I still need a 2m sync cord.
Check out this album for the advantages of handheld strobes: http://lizrogersphotography.com/gallery/al.../mccavity-cave/ In particular, these two photos wouldn't have been possible any other way:
http://lizrogersphotography.com/gallery/al...99/stalactites/
http://lizrogersphotography.com/gallery/al...3/water-levels/