There are some wood gates at the place where my grandparents used to live, that are some 60-70 years old now and are still fine. And they've seen quite a bit of

There are some wood gates at the place where my grandparents used to live, that are some 60-70 years old now and are still fine. And they've seen quite a bit of rain (though probably not quite as much as in PNW). The wood itself matters a lot too. Black locust wood has an enzyme in its grain that makes it extremely rot resistant. I've heard of black locust poles used as fence poles in the ground lasting for decades.