Jimbo, the best protection would be to move it inside where it doesn't rain. Water is your enemy. The questions are how often you plan to repaint or restain and what you want it to look like. If you prime and paint with a high quality (and high priced)paint, it should last 15-20 years. Stain will give you a different look but you will have to redo it in about 5-10 years. Stain is a lot easier to apply. So take your choice. What is more important to you?