I notice that when i deploy the stakes at the start of a battle, an enemy army wiht more than 2 cavalry units will stop advancing, find a hill and camp out on top of it. The AI (so it seems to me) is at least partially capable of circumventing stake useage. Plus the stakes disapear after killing horses so unless you lay down a thick field of them they arent that dangerous. Great for covering flanks/funneling.
IIRC bamboo walls are only available for matchlock units in defence, as in the enemy stack attacks your stack, the same requirement to get the archers deployable walls.
Having stakes, bamboo walls and deployable walls as unit upgrades instead of being linked to a specific unit type would be great.