THIS!
I'M NOT ALONE
Fine, Zapper, I'll help you in your derailment crusades. 
Throwing horses.
Throwing horses you say? That actually seems like a nice way for "horse reinforcements". Basically there's an item (with LOADS of weight, so you move slow as shit) with something like, 10 ammo or something, and when you throw it on the ground, a horse is spawned. So in strat you could get a new horse (have a horse handler at spawn with these throwable items) when you lose the one you spawned with. Obviously it takes 1 away from the horse that the army has or something.
Now for something completely else. What about.... barricades. Not spikes, which someone suggested, or a construction site, which people are using now, but a barricade that can be built from a c-site. It costs around 20 material and has LOADS of health. Tall enough to be unable to jump over from both foot and horseback, but maybe with platforms on one side. Like some of the props already ingame. Like in that desert siege map with the flag oasis in the middle.
Another thing to add. CLIMBING! For ladders and small props. Only works when you are on foot. Probably impossible even with WSE, but maybe when they are done with Project Obvious: The Sequel (M&B 2 for those who don't know about it)
