This BP agent is dragging old tires along Border Road, a dirt road just inside the fence. This is commonly done at dusk, to erase footprints. Agents check the road again at day break, looking for fresh footprints. The migrants are well aware of this practice, and will walk backwards across the road, so their footprints indicate a southern direction into Mexico. This cat and mouse game is played out daily along the border, 7 days a week, 365 days a year.