This seems to mostly be about trolls destroying his buildings. As far as I've seen, no mob attacks your structures if they can attack you. You are always the preferred target. So if a troll raid happens, let the trolls see you and they will give chase; lead them away from your buildings. (They do have AoE's; make sure they're far enough that that doesn't hit anything either.) Might want to refrain from killing them until the raid ends, otherwise more just spawn to take their place.

When I first started playing and got some greydwarf raids, I would jump on my roof thinking I could just snipe them from there. The greys promptly switched tactics to smashing my stuff. I lost two rafts that way. I quickly learned not to cheese them to avoid them anymore. :)