Ok, your boards probably won't be too bad off, although they will last longer if they are protected by regular painting.
However, your posts could rot quickly if you do not paint them. Pressure treated posts are pretty sturdy on the outside, but the inside part of them is not. As soon as you put a fence in and then saw off the tops of the posts to make them even with your top fenceboard, the untreated center part at the top of your post is exposed.
I have found once painted you will either have to repaint depending on you weather conditions every so many years to keep it tidy looking or let it wear off. The following is a link to our oak fencing that was put up around 12 years ago. There are a couple of pictures of a oak fence line that was put up recently. There is also 1 picture of the original split rail that was on the farm when we bought the place. It is over 25 years old. The paddock is used for the retired horses that don’t “test” it. I have not found oak to last that much longer painted. The cost and hassle IMO don’t justify the maybe few extra years you will get out of it. http://s1136.photobucket.com/user/gu...?sort=3&page=1
That is why true fence builders dig holes. Pounding and sawing, you get what you pay for...
I am not sure where you are located or what kind of fencing is installed in your area but around the mid-atlantic region where a lot of horse fencing is installed just about all posts are pounded. If not it is because the installer did not have the equipment. By and large rocks are not an issue. The odd times rocks are encounter a hole will be drilled. By far posts that are pounded in stay secure and straight far better then posts that are set in dug holes and tamped. I state this having done both. It’ a lot less labor intensive which saves on installation costs. There is no sawing involved because all of the post are set at the desired height.
Thank you for the photos, Gumtree. Your fencing looks really nice.
My experience (which I admit is somewhat limited) with drilled vs. pounded posts is as Gumtree stated. The posts that holes were dug and then tamped are not near as solid as the post that were put in by pounding.