I did have various large Dive knives after i started and i did Strap them to my leg ( i didnt use a lanyard as that was obviously a snag hazard)
After getting fed up with it snagging in Weed etc ( its like a barb on a hook) and after getting stuck on a Lobster pot line for a few mins in a raging Tidal current where it was difficult to bend round to get the knife handle off due to the force of water and my Buddy had long gone as you cant stop I did get free as the knife pulled out and was lost I fired up a DSMB and surfaced.
Once i started technical Diving on Deep wreck penetration it was obvious that a leg knife was a liability and probably out of reach if you did need it as it would be the cause of the problem.
A safety dive knife has only one purpose to cut you or your Team out of a tangle ( rope or more likely Mono line net you cant see) or cut you or your team out of the BCD/Harness
so a serrated edge is essential as what ever your cutting is usually next to and can be tightly agaisnt a bit of body you dont really want sharp points or a double edge this is a stress situation so panic/ shock is also a factor when a blade stars getting waved about at your main Artery even a cut in a dry suit could be fatal if your in cold water and have 1hr of Deco to do before you can get out.
Bushcraft stainless is a high carbon stainless which does rust and a fine scandi edge is delicate and more prone to rust
Dive knives are generally a cheap basic steel with better rust resistance that edge holding as they should only be used in an emergency that said mine still shows rust in the handle which i strip and clean then grease a couple of times a season
best mounting place is on the belt to the left of the buckle where both hands can get it easily its small so wont get in the way should be secured but not a lanyard checked regularly but only taken out for serious use
Mora Did infact make a Knife that a lot of divers used but haven't for a while it was basically the same as the electricians knife (see pic ) they do now but with a serrated edge
not very macho but works well
you could get the mariner serrated blade clipper and grind it back to make a good rescue blade
i use a small BCD knife thats cheap
same as this but I use a cordura sheath with a rubber band to hold it in
get the forester use it for bushcraft use and enjoy
but get a dedicated Dive knife enjoy the fact you may never use it if you need a pry bar or other take a separate tool.
I cant comment of Surf blades Ive never done it, leg mount maybe a sensible option
ATB
Duncan