Do walls have durability while NOT being attacked? I noticed some walls I put yesterday today had a 1/4 heart... which if they had durability under normal circumstances, that seems a bit fast to degrade.
Then again, maybe they -were- being attacked? Do the unfriendly NPCs attack your fortification? And do they steal your things? (which... would be kinda annoying yet cool if they could steal when you leave doors open) XD Because I left my door open today and one ran in and out... lol I didn't really notice anything missing tho (even all my crops were still in the ground).