I have a problem against assassin using races in midgame wars. They often have massive archers or longbowmen defending their cities, and siege or casters are often necessary to break the cities defense. However, even when I build 3-4 siege units to go along with a stack of 10 or so normal units, the AI will suicide assassins against the stack and kill most of the catapults. Are there any units that prevent assassin from targetting the weakest unit? Or do I have to build something like scouts and put them in the massive stack so that they feed XP to the assassins instead of the catapults?