Hey all. I'm building a raised planter bed as a gift with salvaged kiln-dried pine. I know that using poly wont last as it will flake and bubble in the UV light. Would a spar urethane do, or would the chemicals leach into the soil and possibly harm the plants? It's probably only going to be flowers in it, not veggies so i'm not worried about eating anything nasty. Any input would be appreciated, thanks.