Personally I doubt than any finish will withstand several years of our winters..without redoing the finish every few years....but I went along with what info I could gather on the web and what the finishes said on the cans...I used teak oil on the fishes and the spalted maple first...several coats...I used a an outdoor spray paint...primer first...three coats on both sides then three coats of outside black spray paint on the backer before glueing with Titebond 2...Also used screws on the backer besides the black screws in the fishes eyes for assembly...kinda doubt if the glue by itself would hold up to the cold. Krylon outdoor satin acrylic spray finish on the backer...both sides before assembly...and about 6 coats of it both sides of the piece after assembly...Crossing my fingers...I did tell the guy that putting it in an alcove where its not getting direct weather will help it hold up longer.
Only time will tell now.....
Lin