We're 2,000 feet above the coulees and gaps that split the prairie on Montana's northern tier. It's easy going and today the air is calm.

Still, the OH-58 helicopter, an Army green machine about as spacious as a Volkswagen beetle, dances on the evening currents rising up from the arid landscape below.

The pilot does this for a living, riding the wind. He's one of a few in the Montana National Guard dedicated to intercepting drugs and illegal immigrants on the border and elsewhere in the state.

He holds the joystick like a motorist holds the gearshift at top speeds while running down the highway on cruise control. That is, he's hardly touching it.

Below, the prairie gives way to a forest of aspen. The ground rises up, meeting the hills of the Glacier National Park. That's when his voice crackles over the headset and his fist tightens over the controls.

"Did you see that?" he asks.

Before I can answer he's banking sharply around. The helicopter turns so steeply the force of gravity pushes me deeper into the seat. The pilot had removed the doors before the flight, so now I'm staring at the ground 2,000 feet below, held in by a flight harness.

I press the button on the floor, activating the headset. "What is it?"

"A road," he says. "Hold on, I'll circle back around."

He makes the turn again, this one as tight as the last. I didn't know helicopters could fly like that. He proves they can.

The road is hardly a road at all. Rather, it's a two-tracked trail running north from Canada across the border, where it snakes around and disappears into the trees of Montana and the Blackfeet Indian Reservation.

It's just one of several roads spotted on the flight. The pilot has seen them before, or at least others like it.

In fact, he's even seen aircraft fly illegally over the border, only to watch them return north shortly after. With pontoons for a water landing, they're suspicious to say the least.

"They probably just drop their package," he said. "I'm not fast enough to keep up with them. I can't force them to land. All I can do is notify the Border Patrol."

While an effort is being made to secure the nation's northern border, the number of those working here, both in the air and on the ground, is far too small to win the battle. As the pilot notes, it's a matter of being in the right place at the right time.

Drug smuggling aside, a group of dedicated terrorists could slip across the border with a little planning. It's a good thing they haven't discovered it yet. But in time they could.

"We shall come at you from your front and back, your right and left," Osama bin Laden warned on the anniversary of the Sept. 11, 2001, terrorist attacks.

In the meantime, the nation continues to rely upon deterrence for its future safety, hoping it's enough to keep the wrong people from infiltrating our city streets after sneaking across our sparse frontier.

Reporter Martin Kidston: mkidston@helenair.com or 447-4086.