Follow the contour of the ground and keep it the same hieght from the ground all the way around your property. I bought my boards from the saw mill, set my post in concrete but first I put tar on the end to be submerged in the concrete.
I had to buy a special permit for a 8 foot fence because the house behind mine is higher. Keep you sections or you post within about 8 feet of each other for the strength.
Mine has lasted through about four hurricans now, when I've seen all my neighbors fences that were two feet shorter crumble. It's been up about ten years now, well worth the 2,000 dollers it cost to build around a 1/4 acre. Took about 3 days with letting the post set up in the concrete for a day. At the the finish I measured the boards then snapped a chalk line along the top then went along and trimmed it with a circular saw. Kurt