I strip the bark off to allow the round to dry out easier. I then use some old oil, (any type would be fine), and put it on both ends till it stops sopping it up. When it needs it - every year or two - I'll slap some more oil on it.
Wood, if it can dry properly, will last a very long time. Ever notice the vertical boards on an old farm building? Some are over 100 years old. I have a bunch that had the softer wood just wear from the elements. The harder will not wear near as much, and the results are quite nice.
Actually I have some boards that were siding for well over 100 years. They are somewhat fragile. I made a kitchen table from some. I covered it with many coats of polyur - enough to fill all the grooves and make the top smooth.