I've certainly had big animals spawn inside both my trap fence surrounding a single tile lake, the trap line surrounding my homestead, and the one surrounding my farm plots, and this for a homestead bordering rapids. When it comes to Njerps, they can recognize trap lines and proceed to disable the traps (I had one that knocked out about two dozen traps, snuck past my charancter's back when he restored a trap (I saw something move in the corner of my eye, and later saw the foot prints), to disable another half a dozen traps. I did eventually kill him, though. I've also (with an earlier character) been invaded by robbers who waded through freezing cold water to climb my fence bordering the lake rather than the fence lined with traps on the inside. Unfortunately they didn't seem to be bothered by the cold, but somehow my character actually managed to kill them all in a desperate fight literally at the doorstep of the house.