Alright. This is an exercise in futility, but ok I'll play. What would I do if I was in charge of the security response if Mexico started lobbing essentially unguided missiles into Southern California?

(I would assume that there would be an active diplomatic team, doing things like sanctions and all the usual non military types of pressure, so that's somebody else's job. As chief of imaginary security, what i would do is as follows.)

1: Assemble a large strike force comprised of Delta Force and other special operations types, as many as I could muster. They would be in small fast planes and helicopters for fast response. These teams would have to be kept in a state of constant high alert. I would enlist some heavy low-altitude air power, probably "Spooky" AC-130's, for close air support of the special forces. The Spookies would be operating under very very tight fire discipline, and would only respond with highly targeted fire if the special forces folks came under attack.

2: Assemble on-the-ground intelligence gathering teams. Fortunately in this case, Mexico is riddled with US intelligence assets, so they would merely need to be contacted and activated, if they havent already been activated. I would also place snatch and grab teams on the ground so when we get a tip that somebody is actively involved in the attacks on Los Angeles, we could grab them and start interrogating, and start pulling in their networks and cells.

3: Heavily surveil the area that the missilies are being launched from with low altitude spy planes, like the Centra Spike ones that we used to target Pablo Escobar.

4: Support those spy planes with higher altitude, heavier processing-power spy C-130's. (I think theyre called AWACs.)

5. I'd drop cheap walkie talkies or cellphones by the hundreds of thousands, that are directly wired-in to an intelligence processing center. I would leaflet the countryside with propaganda, and encourage people to report when they see a missile battery being erected in their neighborhood. I would institute a massive reward for US sympathisers in Mexico who help take down a missile battery or terrorist cell. The intelligence processing centers would do the difficult job of weeding out extraneous or frivolous calls.

Between the large amount of ground intelligence that would be gathered by our army of bartenders, taxi-drivers and the like, and the vast amount of data that would be generated by the Centra Spike and AWACs planes, we would have enough information to begin targeting the missile batteries. As these are essentially unguided missiles with low payloads I would try to keep my cool as theyre launched, knowing that the chances of heavy damage would be minimal. We would also have moved anti-missile systems to the border to help combat the missiles.

When a missile is launched, we will have instantaneous information on exactly where the missile was launched from. The special forces and the Spookies would be immediately dispatched, and shortly, and without aerial bombing, the missile battery would be taken out, and those people who were operating the missile battery would be either killed, or preferably captured and interrogated. No buildings would be destroyed. The interrogations would conform to international law. We certainly would not wipe out the neighborhood with artillery barrages or aerial bombing, because A: it's a lousy thing to do; and B: it would make the intelligence gathering much harder, if not impossible.

Anyone firing a missile would know that within minutes of the firing that they would be in custody of our armed forces.

In the meantime, hopefully our diplomatic team would be hard at work, and the international community would be assisting in the diplomatic efforts.

There'd be a lot more to it, obviously, but that would be the general idea. This is essentially what we have done again and again, in places like the Phillipines, Colombia, Honduras, Greece, Hungary... The list goes on. It aint rocket science.

Once you start indiscriminately bombing cities out of existence, you'll have no choice but to either give up and pull back when you find yourself diplomatically and militarily isolated, or you'll have to commit to World War III, and kill every last man woman and child in Mexico, cause it will never end.