After I finish wet molding the sheath to the knife and it is dry, I melt a stick of parafin with a table spoon or so of saddle oil and when liquid, apply it to the sheath inside and out. I heat it with a hair dryer to open the pores of the leather to let it permeate the leather. It makes the molded sheath rock hard and impervious to the elements. When needed, you can just re-apply. It works great for me and I've been doing it to sheaths for over 40 years.