One way cattle gates. We saw several of these. Salt blocks and in this case a water tank lure the cattle out of one grazing lease and into the next. I've heard that the Forest Service has strict regulations on the number of cattle and how long they can be grazed on a leased plot of range land. If these one way gates work they would significantly reduce the effort required to round up the cattle and move them at the end of the allotted grazing period..