I've tried several setups, but the best is a Spyderco Rescue knife clipped inside the lower strap of my Trace softball knee guards. It's perfectly secure and comfortable and easy to reach and open with either hand, and has held up well to salt. Best of all: it's compatible with wearing a rash guard over your PFD, which does wonders for keeping your gear from getting snagged on the rigging. Coming in off the wire onto your knees also does wonders for not getting fouled in lines, as well as being much faster.

In my experience, other systems cause problems: fixed knives regularly catch lines or are torn off (I saw one torn off last weekend.). Knives clipped to PFDs fall off regularly. Knives with built-in spring clips foul lines and sometimes clip onto lines and sometimes pop off. Knives with lanyards can get badly fouled. Knives in pockets can be hard to access.

The Spyderco "Atlantic Salt" knife appears to be an even more salt resistant version of the Spyderco rescue knife.