There's several sorts of acids, stronger and weaker ones. Regarding causing rust, phosphoric acid for example is commonly used for removing rust without harming the actual metal. That's also commonly available as it's relatively harmless - actually it's also being used to give acidity to some aliments! Same goes for (white) vinegar, there's lots of vinegar rust removing videos although the standard 5% acidity requires quite a long time to work. Hydrochlorid acid will chew iron faster and can cause rust but for sharpening that might work even better. Dilute it into water to some 20% first and remember the order: Add acid into water, not vice versa! And don't forget the baking powder for neutralizing after having flushed the acid with water. You can also mix the baking soda into some water for added flushing. And finally some ultra thin moisture replacing oil like WD40 or CRC 5-56 to get all water out. A spritz after every use might not be bad in seaside conditions. If you fear for staining, wiping the excess with a dry shop towel and then using alcohol for the residues should keep your precious woods clean.
Speaking of vinegar, how come you didn't try ebonizing the laurel fretboard in another video using vinegar and steel wool?