One very durable combo finish for wood that will be taking a weather
beating is to do a few coats of epoxy first and then use a good quality
marine varnish..with a UV protector if it will be in the sun.  You can buy a
two part epoxy online.

  Depending on the wood species, you should thin out the first coat of epoxy
to penetrate well.  Sand between coats and put about 2-3 coats of varnish on
the top.  You can 'refresh' the varnish topcoat as needed.  We used this
technique at a boatyard where I worked and it amazed our customers.  I have
some oak counter tops in my kitchen that are 12 years old now and still look
almost brand new.

  Pay attention to the epoxy.  It's pretty gnarly stuff..Do keep it out of
your insides..

  Don Hanson