Best way to avoid troll invasion: Don't put any heads on the spawn.

It's just dumb that we HAVE to pretty much do the moat thing, otherwise they completely devastate whatever they touch. I would almost appreciate it if the other enemies did more damage later on because they are absolutely insane. Why would the difficulty spike for invasions be like this? The swamp, plains, and mountain invasions pale in comparison to the Forest one, and that one comes in before you can even get Stone.. ridiculous!