Agreed, if it's straight just do AB line between the corners. Drive it and stick something in tractor's hitch pin that'll drag a trench. Or rig up spray paint can or whatever you want. As mentioned, then you can set a line that's perpendicular to whatever that heading turns out to be, and spaced the distance you want your posts and then it'll show on your light bar and on map where the lines (posts) would be. Stop every time you're at 0. Just have to check your offsets to make sure the front/back measurements are matching where it's putting the line and the person is marking the hitch pin or whatever spot you choose for that measurement