Low maintenance Fence

A lot depends on why you want the fence and how much room you have. Driving around Southern Ontario, I can easily see cedar rail fences that are over 100 years old, unmaintained, and have not fallen down. They don't even have posts! Cedar just won't rot, and they were constructed to be stable, let the wind and snow through, and endure. They take up a ton of room though, and don't hold back anything smaller than a cow or a snowmobile.

So, are you just marking your property line so snowmobilers and hikers stay out? Confining your dog, excluding the neighbour's dog (or cows which have been a bigger problem for us over the years), excluding deer, reminding your kids where your land ends, preventing neighbour children from visiting your pool and drowning, providing shade, providing privacy, cutting the wind, building something to hold up trees and vines... ?

I just had to replace my mailbox. A pressure treated post was put in the ground (no concrete) over 20 years ago. It's still solid, I just had to move the mailbox to somewhere else. The stresses on a fence are higher, but don't get too worked up about "making it last" from a contractor point of view. Design the fence so that if one post does happen to fail (perhaps water pools there) you can disconnect the boards, replace the post, and put the boards back. That will be your most maintainable and longest-lasting fence.