I have discovered (from the YouTube channel below) that fresh water rots wood and salt water conserves it. I guess it makes sense as salt is a widely used preservative. Having been subject to lots of good old Scottish rain over the past 30 or so years the decks have had their share of fresh water. As we progress repairing the decks, the lesson to take from this is regularly and liberally treat the decks with salt or some other more suitable preservative. Suggestions gratefully received.