That is a big field. Have you tried a blind? You can get an Ameristep for $50-$60. May get you a little closer. I know what you mean about them changing patterns. A couple of years ago I hunted a new place for a week. Every day I would hear gobbling (I mean gobbling their heads off gobbling) on the left side of the property and I am on the right side. Five straight days. OK, on day six I set up on the left side and hear them gobbling on the right. Go figure.