Ability to give more specific commands to none seige units

When I am attacking an enemy town, is there a way to get certain units to fo certain things? Such as sending infantry troops to focus on enemy soldiers and leave razing buildings to seife units?

Too many times enemy soldiers have run past my troops who are destroying a random house and taken out my rams.

Ive tried setting them go guard mode and selecting a seige unit but sometimes they dont respond to being attacked as a unit.

Would make gameplay so much better.