The U.S. Border Patrol is locked in a major battle with the FAA (Federal Aviation Authority) over the use of UAVs. The FAA insists that only UAVs that can see as well as a human pilot can be used within the United States. No UAVs have this capability (as it requires mounting several more vidcams to reproduce the view from a cockpit, and more communications gear to transmit all that data). The FAA believes that the many aircraft (plus gliders and balloons) that are in the air, without transponders, make these "enhanced" (with additional sensors) UAVs a necessity. The FAA has the final word on what is allowed to fly in the United States. For the moment, unenhanced UAVs can only fly in specific zones that have been cleared, via an FAA order, of all aircraft lacking a transponder.
Thus the Border Patrol's sole Predator UAV can only fly a 160x24 kilometer area along the Mexican border. The FAA can move the sector, but this is public knowledge, which lets people smugglers know which areas are being patrolled from the air (with night vision devices). To deal with that problem, the FAA now allows the Border Patrol to file its flight plan an hour before take off, meaning that most smugglers would not get the word and would be more likely to get caught if they moved into an area being observed by the Predators heat sensors.
The Border Patrol is getting a second Predator, and wants to expand its search area to 600x24 kilometer, and get permission for the Predators to fly higher than 14,000 feet. Military UAVs with the enhanced sensors are not expected to be available for another four years. These enhanced sensors are not needed in a combat zone, where the military has the final say over what flies. But the military UAVs are finding themselves increasingly used for law enforcement and purely commercial chores. In these circumstances, the FAA is willing to allow them to fly if the operators can keep them in sight. This is usually possible, but ultimately, the FAA will probably insist on the enhanced sensors for anything flying within its jurisdiction.
The Border Patrol now plans to get around the FAA restrictions by using blimps (aerostats, actually). These would be similar to systems already used in Iraq and Afghanistan. There the RAID (Rapid Aerostat Initial Deployment) blimps float at about a thousand feet, tethered by a cable that provides power and communications to the day and night cameras up there. RAID is vulnerable to ground fire from rifles and machine-guns. Iraqis, in particular, like using the RAID blimps as targets. Rifle fire won't destroy the blimps, but does cause them to be brought down more frequently for repairs. Normally, the blimps can stay up for 30 days at a time, but the bullet hole repairs have some of them coming down every few days. There are surveillance systems similar to RAID, but mounted on 110 foot steel towers. These also suffer gunfire damage, but rarely any that damage the equipment. RAID cannot cover as much ground as a UAV, but it does get around FAA concerns.