The U.S.-Mexico border has been a defining theme throughout the 2016 presidential race. The candidates are divided: Trump has focused on literally building a wall; Clinton talks about creating a path for undocumented people to apply for legal status.

Meanwhile, those who are actually tasked with patrolling America’s southern border have been reworking their ground game, as drug cartels increasingly turn to drones to ferry illegal substances into the country, CBS News reports.

To keep an eye on drone smugglers overhead, border patrol has six huge blimps equipped with low-altitude radar that can detect aircraft flying too close to the ground for conventional radar to spot. The blimps are called Tethered Aerostat Radar Systems and are filled with helium to elevate them to an altitude of up to 15,000 feet, moored to the ground with a single cable. TARS are essentially surveillance devices.

U.S. Customs and Border Protection has been using its own drones since 2005 to patrol America’s boundaries. It currently has nine drones, reported the New York Times, that can fly at speeds up to 275 miles per hour. By comparison, most drones available for sale in stores max out at around 22 miles per hour; these border aircraft are winged and about the size of a small plane, but they fly unmanned.

A drug-smuggling drone carrying 28 pounds of heroin was intercepted after crossing the U.S.-Mexico border last year in what was considered to be “the first international narcotics seizure by U.S. law enforcement involving the use of drones by Mexican drug traffickers," read a statement issued by federal prosecutors.