I use hay bales to my advantage quite a bit. For one they are great to use to stalk. Line the animal up with a bale and move in closer you may be 60 yards from the bale but they cannot see past that big round thing. I often just sit behind one and hide if i am sure the deer are coming from the other side and will not walk around to discover me. I also like to take the tractor and put 6 or 7 of them in a circle close togther making a blind with 4 or 5 shooting windows where one bale meets the next. My buddy uses square bales quite a bit and that seems to work well also. It sucks when they start eating your bales though.....