Perhaps the most common wood preservative available to DIYers, oil-based copper naphthenates are classified for general use by the EPA. It's commonly used as a brush-on preservative for end cuts ...

PenaShield Clear Wood Preservative is a notable example ... go with Rust-Oleum’s Woodlife CopperCoat. Another copper naphthenate, CopperCoat doesn’t contain any tinting to hide the green ...