I've recently started doing some inlay for fun. One of my first inlay projects was a belt buckle made out of walnut that also contains a little bit of marble wood as well. I like the deep toned natural look, so I just finished it with some mineral oil. This is fine for me because I can easily apply more after sanding down a nick or a rough edge from getting wet. However, someone has commissioned me to make one for them, and I need to come up with a more durable and waterproof option for a finish. I don't mind a little bit of gloss, but I'd like to keep somewhat of a natural look if possible. What are my best options? Is it something I would have to special order or could I pick it up at a local big box hardware store?