How about a scouting penalty while raiding? I doubt there were volunteers willing to give up the chance of plunder to screen for enemy forces, especially in smaller forces. What about an option where a larger force within a certain range is given the option to attack a plundering force with a detachment. The type of troops selected to sally forth (troop type, skill, leadership etc.) will determine the enemies willingness/ability to flee or fight. Fleeing in a rush could result in leaving behind a portion of the men and loot while fighting off the advance force could either buy needed time to escape or give the main army time to reach the village (represented by a slow trickle of more troops onto the map.)
Bjorn the Hound mentioned the recruiting mechanic above (specifically where AI lords and the player compete for soldiers). I hope there will also be an inflation mechanic that is also tied to desertion, maybe counteracted by leadership strength. Being able to adjust troop wages would be necessary I would think. Higher wages, higher morale; higher leadership traits, higher morale and vice versa. High relationship with the Lord will give better and more recruits but gold should be do the same! Leaders offering much higher than average wages should find hedge knights and peasants alike flocking to enter their service.