Jacko = Ringnoob!!11
There's a button to change the angle on the top row (2nd from the left) of buttons you have for basic commands.
Also, you can click the right mouse button on a scenery object, select properties, and adjust the angle with a convenient slider.
In case that wasn't the question and I misunderstood, please ignore it.
Main advice would be, if you really want to block things, is to use a map which lends itself well to that purpose, has narrow corridors and the likes. The landslides may come in handy perhaps as well; they cover more length than a Kami or Karavan fence. And then there's clusters of trees, buildings, but ofcourse that all depends on what you're planning the map to represent.