Due to the constant phenomenon of my animal followers and human thralls been killed by a boss who appeared out of the blue or brought by a player few times outside of my castle 's walls out of nowhere I decided to use archer thralls from the top of the wall were can be safe from anyone.
whats also fun, is to put archers high enough to shoot and be unreachable, you can even stock them with a mixture of healing and starmetal arrows, they heal ground fighters and do good dps. I always use that for purge events.
Just go to bows and sort by damage or penetration. Reach of the Red Mother is the best combo of damage and armor pen. It also is pretty easy to get on either map.