It's a 5,525-mile (8,891km) border, with 8,000 obelisk monuments dotted along it. These are cast-iron and stand five feet high, on a three-foot concrete base. Cleaning and maintenance is usually in the hands of eight field officers but seven of them have been told to stay at home. That leaves acting commissioner Kyle Hipsley on his own. Speaking from a field office in Montana, he said everything was under control.