You will also notice that, as a player, I can get up on the back side to fight from. On the second charge I attempted to jump the horse up on the barrier, with the result being that I was not thrown. What is not shown is that on another attempt I jumped the horse earlier which result in my being thrown up on the barrier. At no point did the rider take any damage from being thrown or hitting the barrier.
The heavy warhorse only took a little bit of damage from hitting the barrier (which is also not shown). Further, you do not get the option to build the barrier on sand, but you do on normal and forest soil. This allows you to 'move' where you want to build the barrier down over sand.
Spoiler
You Tube: http://youtu.be/wXtKUEWEJQE
I miss u Azzerhoden 