I use a Rob Allen stringer, which has a big, long, stainless steel pin (something like the end of a spear), and a thick, plastic covered cable. The end loop has a loop with a large game swivel attached. Just a regular float stringer, although quite big and tough (like most RA gear), no doubt for the large SA fish. I attach it to my solid RA float with one of the stainless tuna/orca clips, or to my inflatible float with an old, anodized, Welsh, Clogg karabiner (originally designed for sea cliff climbing).
The sharp pointy end, I keep sheathed in silicone tubing (an off cut from Portland Oceaneering) which is tied to the float-end of the stringer. This stops the stringer dangling down too far & stops the point digging into the back of your leg as you walk out of the water!

(Thanks for that tip Miles

). I also thread fish through the gill and mouth as Miles describes (the gills alone looks insecure).
Crawling about in shallow waters yesterday, Indian style - as OMD described - made me think about not using a float in such conditions (although the crab bag & stringer caused more problem than the super light float). A minor inconvenience rather than a big deal though. A fishing boat came by -- so even early morning in the shallows, you have to watch out.
Having a fish on a float or belt stringer probably helps attract fish (camo, blood, fish oil). There is a great picture in one of the spearo catalogues of a guy doing aspetto with a belt stringer full of fish half hiding him!
Belt stringer in action (video clips): Omer - it's probably Spaghetti or one of his mates
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Omer - incs. a 2fer1 shot.
I used to think a belt stringer a bad idea - something else to snag/get caught underwater and, in more shark infested areas, draw in sharks. It doesn't seem to be much of an issue in the UK though. I suppose as long as you can cut it (i.e. mono or cord rather than steel), it could be quite useful. Float stringer seems a safe bet to start with though.