As with all knives they must be cleaned and maintained at all times. Always clean your knife after every use. Never put an unclean knife back in the sheath. Do not use harsh chemicals or dishwashers to clean your knife. After the knife is clean lightly wipe the blade with a suitable oil like mineral oil. Its food safe and non staining. Some handle materials can also benefit from oiling. 

The leather sheath will also require maintenance from time to time. Clean the leather with a good quality leather cleaner. Test a small area first in case of reaction. Once the sheath is dry use a leather balm or conditioner to nourish the leather again. This will prevent the leather from drying out and cracking over time.

Do not store your blade in the sheath for extended periods of time as it may rust due to the leather absorbing moisture and the oil from the blade. If you are storing the knife remove it from the sheath and keep it separate. Wipe the blade down with oil and securely wrap it in baking or grease proof paper.