In Imperial Beach, ever since the fence went up, the “tourists are coming in droves, and more people are moving in than out,” the Times reports, and “grateful residents say the stepped-up vigilance has all but sealed the once popular smuggling routes across their beaches, parks and backyards and helped revive the area’s economy and improve the quality of life.”
I noticed looking at this map that in order to invade the US by this route, you practically have to run through a couple of Naval Reservations, I.E. Imperial Beach Naval Air Station, and the Naval Radio Station north of it. (You can see this if you zoom on the map.) Further north, you come San Diego, which is just wall to wall Navy. So if you're wondering if troops are ever going to be on the border, they're already there. They just haven't been ordered to do anything. Busy elsewhere, perhaps.