A knife sheath is a case that protects and stores your knife and is made of wood, metal or leather. The sheath will allow you to go from place to place with the blade stored safely, while protecting the knife from the elements and any damage that it might incur. Yet, for the knife sheath to do what it's supposed to do, you must know how to use it first.

Put the knife in to the sheath blade first. You'll be hard pressed to find a sheath which isn't designed for the knife to go in blade first. If you do, you probably shouldn't buy it for safety reasons.

Zip, snap or push your knife into place. Different knife sheaths have different closing methods. With some nylon knife sheaths, you zip the knife into them. A zip-up knife sheath makes it more difficult to remove the knife from the sheath. Think about how quickly you need to retrieve your knife when choosing your knife sheath.

Move around a bit to test the knife sheath and make sure your knife is securely in place. Once you are out on a boat or deep in the woods using your knife, it's too late to check the sheath. Activities become harder and more dangerous without a fully functional sheath.

Sheaths built to hold scuba knives generally have a locking device which locks the knife in to place when you firmly push the knife into the sheath. Unlocking only requires the push of a button, so the knife is still easy to get quickly when you need it.
Make sure you get your knives, sheaths and 5.11 Tactical from a quality company. Different materials are suited to different types of sheaths. Scuba knives generally go into a plastic sheath, as this is a light weight water-resistant material.