When/If water gets implemented then I'd want to make a moat around my Fortress err Colony to further make sieges feel like sieges of yore
if and when Water is implemented, there are going to be so many cool ideas for it, maybe a nice garden with a pond, and improvised turrets and mortars, lol
If not moats, maybe canals and waterways, with the duel purpose of slowing down invaders and bringing water to crops.
wooden/electric drawbridge!
XD
What about a way to poison the water? So enemies who walk in it take acidic damage.