Walls work. They slow down possible intruders. Why do you think people fence in their yards or the white house walls off their property. The sensors will alert them when a person is attempting to cross. The wall will give border control enough time to get there. Nothing we do will ever be 100% effective but a wall is a great start. We also need to make it punishable by death to cross our borders illegal Laser carving the earth doesnt because its not possible atleast on that scale