Easiest way I've found is to buy boots that start out "waterproof". Waterproofing leather boots is...at best...a futile effort in my experience. My Cordura/goretex/thinsulate Bass Pro shops, on sale, $70 camo hunting boots stay dry indefinitely (I can stand in the river with them on). My $250 leather Irish Setters with every waterproofing product known to man, do not.