We had a tree fall over and I want my husband to cut me a slice out that's as tall as a cinder block (what I currently use) to use as a meditation stool for my garden. It will stay outside. How can I make it weatherproof? I've polyurethaned some outdoor flower boxes and it wears away and the wood rots. How can I make this solid so I can put in some work, but then never have to touch it again and leave it outside