This is pretty much what I did for my horse fence, though I used 1x6x16 pine instead of oak. However, the half-round posts I used were 6-7" x 8'. If Cobra really used 12-14" PT half-round posts, those would be absolutely enormous and way, way, way overkill, not to mention incredibly heavy.
Somebody already mentioned this, but the really "purdy" fences are usually made of vinyl (or solid gold or platinum coated in vinyl judging by the price).
If you go the wood route, here's a quick-and-dirty contraption I made to hold my chainsaw at a consistent angle to cut off the tops of the posts. It clamps onto the middle of the saw bar and slides along the top rail of the fence.
Josh