Hi Spear,
I use the loop type stringer or s.s. cable stringer. The main point w/ any type of stringer is to make sure the fish is dead BEFORE you take it off the shaft. A knife stick to the brain will do the job nicely. A narrow long blade specially made for this would be recommended. Riffe, esclapez and sporasub all make good knives for this. This accomplishes two things. First, the fish won't be thrashing about sending bad signals to other predators; second, it will stop it from bleeding quicker. I then run the stringer through the gills and mouth then take the shaft out. As w/ everything there's a down side to this method. If there are barracuda in the area they will steal your catch once they notice all those pretty fish hanging there like a bunch of grapes

. Also if you're collecting lobsters, shells, ect. you'll need someplace to put them anyway. If thats a possibility then I'd keep a bag rolled up attached to the float and use if needed. Besides, how are you going to fit a 100# trevally in a mesh bag

.
BTW: I spent a few days on Ishigaki a few years ago. It's a beautiful area. I only got to freedive one day but I'd like to get back there.
Jay