Another great product to harden cloth and cord is nitrate dope.I used to use it to make canvas kayaks and canoes.It is what makes piper cub planes skin hard.You can get it by the gallon at the parts and repair hanger at any private plane air strip.You can probably get it through a major industrial paint supplier,too.You can get it in 4oz. bottles at a RC hobby shop (they use it to harden the skin on model planes).I think it would melt nylon,so test it on your cord it it is not a natural fiber like cotton,jute,or silk.Just brush it on,thinned as needed,and let it dry (it dries FAST).Use LOTS of ventilation.Multiple thinned coats are stronger that one thick coat.