I use the chefs choice electric sharpener. Kinda spendy, but the diamond honed blades are very sharp. You can use a sandstone for honing after, but I find that unless you are very good, you just dull the blade rather than make it better. Not for on the river, but if you take it out sharp, you rarely need to re-sharpen during the day.
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Timbermans motto: The only good tree is a log.