pits and draw bridges

[swillo]

I don't recall seeing this in past posts. but I was thinking that it would be nice to create a moat and or pits around the outside of the walls. Possibly even pits that can be set on fire.

Also we will need to get across them so a draw bridges would be nice.
I have noticed that some of the bridges don't work so well in the environment. I wonder how well placing bridges will screw with the nav map.