Beefed-up enforcement along the Mexican border has made smuggling more challenging for criminal cartels using the major southern routes, but drugs continue to flow across the porous northern border through airstrips like this one as officials look for new ways to fight back.

Tracking rogue planes at low altitude with their transponders off is "like trying to pick a needle out of a haystack," said John Beutlich of U.S. Customs and Border Protection, who oversees air and marine operations from Washington state to Maine.

Tiny airports feel helpless.

"Shoot, we're just a big cherry to pick and didn't realize it," said Joe Allen, manager of the Sandusky airport, 90 miles (145 kilometers) northeast of Detroit.

He installed a fence to keep cars from meeting planes at the runway, but the property is not staffed at night. Border agents could offer just two signs asking people to call an 800 number if they see something unusual.

Homeland Security Secretary Janet Napolitano says the U.S. hopes to start tapping into 22 Canadian radars to fill surveillance gaps on the border. Officials say the U.S. has one national radar network made up of feeds from the Federal Aviation Administration and the Defense Department.

Border authorities also conduct routine air patrols, but some lawmakers would like military-grade radar along with drones that could detect small aircraft.

"All everybody wants to talk about are drug cartels coming across the southern border. I don't mean to diminish that but the northern border has gotten very little attention up until recently," said U.S. Rep. Candice Miller of Michigan, a senior member of the House Homeland Security Committee.

A new law requires the Obama administration to come up with an anti-drug strategy on the U.S.-Canada border by summer.

Canada is a significant source of high-quality marijuana and the amphetamine Ecstasy. More than 2 million doses of Ecstasy were seized on the northern border in 2009 compared to just 312,000 in 2004, the Drug Enforcement Administration said, offering a snapshot of what's popular and what gets confiscated.

Most shipments come by road. But the 2009 flight from Ontario to Michigan, the subject of a recent federal trial, provided insight into drug operations that use small planes. Officials don't know how frequent such flights are but consider the vulnerability alarming.

Matthew Moody and nephew Jesse Rusenstrom, both from Amherstburg, Ontario, were the couriers captured that night in Sandusky. Their job was to enter the country through Detroit, meet the Canadian plane and deliver the drugs to others in the U.S. They also put 60 pounds (27 kilograms) of cocaine worth more than $500,000 on the return flight to Guelph, Ontario.

It was just one in a series of shipments. Rusenstrom said he met the drug plane at least 10 times at other tiny airports in the Thumb region — Marlette, Ray, Lapeer — as well as in Greenville in western Michigan and an airport in Pennsylvania. The pilot activated runway lights from the cockpit, a standard practice in aviation.

Rusenstrom, testifying at the trial of an accomplice, Robert "Romeo" D'Leone, said hundreds of airports were studied on Google Maps.

"We would go around looking for airports, seeing if there was fences or cameras," the 21-year-old told jurors.

D'Leone, who lives in the Toronto area, stopped his trial and pleaded guilty on April 14. Rusenstrom and Moody cooperated, pleaded guilty and were recently sentenced to time served in custody. The U.S. still wants to extradite four others in Ontario who are accused of major roles, including the pilot.

Some jurors were alarmed by the revelations during the D'Leone trial.

"You always hear Homeland Security has an eye on everything. It's surprising that airfields aren't manned 24 hours," Robert Simpson, 47, told The Associated Press.

The Sandusky airport has spent $2,000 on cameras and hopes to install more.

"We're outside radar," Allen, the manager, said, running his finger over a map of Michigan's Thumb. "You can come and go as you please. You don't even have to file a flight plan."

The minimal help he received from border authorities — warning signs — had to be fixed before he posted them: They referred to suspicious boats, not planes.

Beutlich, the senior Customs and Border Protection official, said his agency's routine air patrols "can't be everywhere."

"I don't think there is more than just vigilance," he said, adding that law-abiding users of small airports typically are the best sources to report trouble.