I agree with The Bear. Dive knives should have serrations, in my opinion. While many believe dive knives are for protection against sharks, fact of the matter is more divers have died getting caught up in rope or monofilament than by sea creatures attacking.
I would also recommend a coated blade. It has a higher degree of corrosion resistance and adding to that INFI (which already has solid corrosion resistance properties) and you should be okay.
I am a spearfisherman and actually would like to have a thin stiletto type blade that I can use to place a killing thrust to the brain of a fish on the end of my spear. INFI would be wonderful and I may ask Jerry to build me one someday for that purpose.
Anywaya Ed, one thing I often do is put a small knife under the sleeve of my wetsuit by the wrist, and another larger knife (w/serrations) on my leg. Apply a thin coat of oil before the dive trip, wash with fresh water afterwards, and re-coat. You should be good to go!!