A good sheath is required for a high quality knife. It provides protection against damage to the knife and is essential for safety.
In the past, I furnished a heavy duty leather sheath with each knife. Leather is traditional for a custom knife but it does have some disadvantages. It can absorb moisture, accidentally become contaminated and cause corrosion if the knife is left in the sheath for a few days.
This is especially prevalent in a salt-water environment with fillet knives. I have made the commitment to tool up to make "Kydex" sheaths and will no longer furnish leather sheaths.
Kydex is a thermo plastic that can be heated and molded to the knife. It is impervious to water, the interior can be rinsed out with soap and water and it forms a very stiff lightweight substantial sheath. A very sharp knife blade placed in a leather sheath incorrectly can come right out the side. I have done this myself with a fillet knife when the sheath was bent over to one side and I did not notice it.
This is not possible with Kydex due to the hardness of the material. At the risk of contributing to more plastic in an already plastic world and appearing to be too tactical, I will now be providing a Kydex sheath as a standard with each knife.
It has also been traditional in the past to provide a belt loop on a knife sheath. I am drifting away from this requirement based on my own hunting experiences and from paying attention to what others are doing.
Most fixed blade hunting knives now go in daypacks. A knife and sheath hanging on a belt is just in the way. The knife can be damaged or lost in a fall and the handle pokes you in the ribs every time you bend over or sit down.
My advice is carry a good low cost, high quality (like Spyderco) folder in your pocket for easy access. Keep the higher cost custom knife in a back pack where it is protected and safe until it is needed.