Here's a (hopefully wont go political?) mental exercise for y'all.
How would you start securing the border, starting today, if you had control over DOJ/DOD/DHS/KFC?
The border is 1,969 miles long. I'd start by planting a hesco CoP every half-mile, and manning each of them with a 10 person team working half-n-half 12 on/off. Duty cycle would be four days, upon which time they get relieved by a fresh 10 man team. For two teams per CoP this comes out to roughly 80,000 people, not counting support groups and such. Lets put down a support base/FOB for every 50 miles of border, with up to 500 people per and that brings the grand total up to 100,000 troops. Random vehicle patrols to be provided by the FOB contingent. Each FOB shall maintain at least two armed helicopters that are at a ready-to-fly status for QRF, or pursuit of illegal crossers fleeing in vehicles that the CoP's are unable to catch. Each CoP should have at least one MRAP, a humvee, and any other vehicles as needed and equipped with suitable crew served weapons and thermal/night vision devices.
U.S. Army has about 1.1 million active and reserve personnel. That's a border deployment of 3 months every 2 and a half years, or a 6 month border deployment every 5 years, if we don't cycle in Marine units and other service branches.
ROE:
Engage any armed illegal crosser with lethal force.
Any survivors who surrender are to be turned over to BP.
Warning shots are not allowed.
Any unarmed illegal crosser is to be intercepted by the nearest CoP's, and turned over to BP.
QRF's and random patrols provided from the FOB's are not to stray farther north than 12 miles from the border unless in active pursuit of illegal crossers.
ETA: further/farther.
Second stage after establishing a presence on the border would be to convert the rapidly deployed hesco CoP's to more permanent and secure earthen dammed reinforced concrete structures. Observation and weapon tower, below that the main bunker, and connected off to the sides would be the bunk room and hygiene facilities (a real bathroom, with real showers, not the conex crap) and a secure enclosed motor pool. Fairly simple and small (relatively speaking) structure. Power, water and sewage provided off local utilities where available, and installed as needed as part of the temporary to permanent conversions.