If you do use concrete around your fence posts, go to any place that sells re-bar, and you should be able to find rebar twisted into a circle and the ends welded together. They are very inexpensive. Drop one of these over your fence post every couple of shovel fulls of cement and it will prevent the concrete around your post from cracking radially.
Also, taper the top of the concrete so that it sheds water away from the post, and cover the concrete with plastic while it cures. That will keep water from evaporating from the concrete, and the result will be that the concrete will cure harder.
And, when I built my electrified parking fence, I tapered the tops of the posts by cutting both sides with a circular saw set with the blade at a 10 degree angle. Then, I had "roofs" made of 1/8 inch thick plate steel and had them bent in the middle to a 20 degree angle and glued them to the tops of the posts with LePage's PL Premium construction adhesive. Those steel roofs keep rain water from getting into the tight crevices where the fence horizontal pieces attach to the posts, since it's water getting into those places and pooling there that results in wood rot. The bigger the "roof" you can put on top of each fence post, the dryer the post will be and the less liklihood that you'll ever have any wood rotting on your fence.