I've been reading the blogs lately about putting Guradsmen on the border and I started doing a little research. Wikipedia tells us the US-Mexican border is 1951 miles long. We'll use that as a planning figure. If you want Guardsmen to watch the border, you have to assume that they will use standard infantry companies, or a reasonable facsimile to do that, so some basic math ought to give us the manpower requirements.
Current doctrine says that a rifle platoon can observe and control 750 meters of the FEBA under ideal conditions. That infantry commander will probably adopt a two-up, one back configuration so that the soldiers on the line can rotate out, rest and re-equip regularly. With two platoons forward, assuming ideal conditions, we can assume that a rifle company can control 1500 meters of FEBA.
A mile is 1609 meters. The whole border is something over 3.1 million meters. Divide 3.1 million times the 1500 meters that an infantry company can handle, and we learn that it will take 2067 Infantry companies to secure the southern border, from end to end. Depending on the TOE, there is something like 48 rifle companies in a division. (4 brigades, three battalions each, four companies each.) It'll take 43 divisions, linked shoulder to shoulder to secure the southern border. We don't have 43 divisons.
I retired from the LA National Guard in 1999. This plan is a smokescreen for something else. We don't have the manpower to immediately secure the border.