This is such a ridiculous comment. It has never been in the technical capabilities to seal off any land border in the history of humanity, because any controls

This is such a ridiculous comment. It has never been in the technical capabilities to seal off any land border in the history of humanity, because any controls that you can put in place, including all of the technology that currently exists that you could throw at it are still designed by humans, require absolutely no collaboration on the part of the operators of those defenses, and are immediately upon deployment subject to attack by your adversaries. Assuming you are referring to the United States, even if you deployed all of those sensors at all crossings, it would not be sufficient to deter crossings; those only provide detective capabilities. Yes, you would radically increase the number of people guarding the border, but that would also require a radical investment in enforcement, and such an investment would bankrupt the country for no real practical effect. Even if you did fund and build it, the maintenance costs of preserving the effectiveness of such a land border along the northern border with Canada means protecting a nearly 9,000 km border that about 200 km from the West Coast turns into extremely inhospitable to hostile terrain and climate for a minimum of three to four months out of the year. This terrain is absolutely awful to stalk and patrol in, but is a pleasure to sneak through (at least I really enjoyed it back in my hunting and military training days :D) It is not feasible to scale the navy to the point where it would be practical to prevent access to the continental United States, for example, let alone the island territories. Attempting to do so would bankrupt the nation. Hell, modern technology can't even reliably prevent folks from bobbing over from Cuba despite the relatively small attack surface there. Even if you managed to invest more than the current percentage of GDP (which is already ridiculous), you would also have to confront an increasingly hostile domestic population who is used to freedom of movement, is already paying punishingly high taxes in contrast to the value and benefit they receive for them, and rapidly diminishing quality of life. Good luck with that! Oh, and one last note about capability based security - it works great in lab and somewhat small environments, but I would appreciate a practical explanation of how you would scale up capability based security to an environments operating in 87 distinct countries (with disparate regulatory requirements that preclude centralized management), 3600 offices, and 800,000 employees, with approximately one third of those employees having employer managed devices, notebooks, and managing a total of 2,300 distinct software applications (granted it's been about 14 years since I worked in that environment, but that company has grown substantially since then). I'm listening for a real, practical suggestion here, not being facetious.