Fair points and I agree that something like that would have been a good approach, but the problem as a whole is that the settlement was barely developed or organised yet and the defence as a whole was haphazard and very short notice (and frankly the OOC planning of the battle wasn't handled very well either, but let's not get into that). I'm not sure the pre-knowledge of the enemy's movements, the organisational ability, time and resources were really there to make an elaborate defence. But maybe I'm just making excuses for my lack of creativity.

This does make me wonder if the cult includes war time engineers/sappers though, I hadn't really considered that.