I carry a "rambo" knife, outside, right leg in a very low-profile scabbard....as soon as I hit bottom, first thing I do is pull it out of the scabbard, slip the attached lanyard over my wrist...use it for probing tapping, prying, butt for hammering. Very dull, I can grab it by the blade with no worries of cutting myself....., long, broad blade that you can use for leverage when you're prying...more like a tool than a knife. It also has a line cutter for small stuff like mono. I also use it to hold myself off the bottom as a pivot point. I have a VERY sharp knife attached to my BC strap next to my power inflator...only used if I need to cut a heavier line....I also have a pair of EMT shears in my BC pocket, right side. When you ask a question like this, keep in mind that there are hundreds of different kinds of diving scenarios.....try a couple of variations and come up with a configuration that works for you with the kind of diving you do.