Dive knives are designed to be tools not weapons, dive fashion accessories, or used to make a statement. Their primary purpose is to cut yourself out of an entanglement from fishing line or kelp or anything else. They are not used as a defense mechanism against marine life. Strapping a large knife to your leg is probably more of a detriment from possible entanglement than a good thing. The ideal knife should be small, sharp, and short and carried in a pocket or on the waist belt of your BC in a sheath. This way, it is easily accessible in case of an emergency. Some knives have blunt tips that can be used for prying objects or used as a screwdriver tool, serrated edge that can be used for sawing and cutting through line, and a line cutter. Spearfisherman use knives to kill their catch underwater so that they stop struggling. Many spearfisherman carry stilettos or small daggers for this purpose.
Line cutters and scissors are used primarily for cutting line. Line cutters have small hooks with razors that grab and cut the line. Scissors are used just like standard scissors and can cut line, kelp, or just about anything.
Cost: $15 to $100