sorry ppl, i got misunderstood, i will rephrase:
i manage to make the trolls dmolish walls by clicking on them (The little bow appears with a green arrow). they do as they are told and throw stones until the wall is down. but when it is an AI player assaulting my castle, he wont use the most eficient attack, which is throwing stones. After a bit of observation, i noticed sometimes they do throw those stones at gates only, but only once, then they storm the gater by force...
anyone managed to make this work?