How to Preserve Wood in Raised Garden Beds

Would like to make some of my garden into raised beds - for my back. Working with organic gardening, so it is said that we should not use treated wood. Well, bricks also leach bad things into the garden. Can't think of anything else to use. Suggestions ?? Thanks
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Made from naturally occurring plant and mineral extracts, this wood preservative penetrates wood fibers to provide protection from sun and water. A single application results in a long-lasting, maintenance-free surface