My first thought was the necessity for these new border guards to be armed. Thus, I see the potential for a number of unfortunate shootings as a result of the lack of quality recruits entering this new civil service. They would need to be very well trained before being unleashed.
It's one thing to mold a Marine recruit to kill in a foriegn land. Quite another to unleash a less qualified individual on our own soil toting the same weaponry...or close to it.
All of which can be dealt with by selecting quality applicants and training them properly.
Frankly, I see no reason for all of them to be armed. Modern non-lethal defensive weapons would be sufficient. An armed special unit could cover any situations where arms may be needed. (regarding the Mexicali's)
try not to think in military terms, but more along police and security lines.