Nothing is impregnable.
But that beast will just deter most people. Thirty feet high is the roof of a three story building - almost a fourth story windowsill. It is a dizzying height. Few people would attempt such a climb. Getting over the huge barrel top requires relying totally on the rope, while your weight keeps it pressed down, and switching to another rope secured in the other direction. You risk falling to your death on either side. It is more of a job for a circus acrobat or Tom Cruise's stuntman, than a farm laborer, or one of the guys in front of the Home Depot.
The highest barriers today are eighteen feet. Almost no one who falls from eighteen feet will die from it - people overwhelmingly walk away from it. Thirty feet kills most, and the injuries are correspondingly more gruesome.
Along with that barrier, there is patrol road for fast police response, and typically lights, direct observation by high magnification cameras (as folks first begin to approach the barrier in Mexico, with their bundles of rope), and sensors that serve as alarms, in case the attention of monitors lapses.
In dense urban areas, getting over the first barrier only gets them into the no-man's land of the enforcement zone, where they are caught between two such barriers. In rural areas, they are likely detected, and engaged in a long range chase with them on foot and Border Patrol in vehicles, subject to tracking by aerial drones.
It is hard to get a sense of the imposing nature of these barriers from a picture - they tower above the pedestrian like a cliff. More than the top ten feet provide no finger or toehold, and the girth of the barrel top is far to great to grip. The large obstacle at the top is key to this design, simply making a straight climb up a pole twelve feet higher would be of marginal utility.
These barriers dwarf the pedestrians.
