With all the attention focused on controlling the US-Mexico border, it's easy to forget that America has a much longer international line to the north. It includes some of the roughest terrain in the West: a 500-kilometer stretch along the Washington/ Idaho/ Montana border with Canada. U-S Border Patrol officers use an old-fashioned kind of horsepower to monitor the territory -- the kind with four legs and a saddle. The goal is to stem the tide of people, narcotics and even terrorists.

Since the 9/11 attacks, the U-S Border Patrol has beefed up surveillance along the Canadian border. Stiffer monitoring on the ground and in the air is readily apparent in well-populated areas. Agent Lee Fitzpatrick says that may be driving some of the traffic to this uncharted wilderness. "Whatever position you take as a front against a criminal act," he points out, "your criminal mind will always look to the weakest point."

Fitzpatrick and fellow border agent Steve Kartchner are part of a program that began earlier this year. It's an effort to discourage attempts to exploit this remote, rugged terrain. Open field soon gives way to dense woods. It takes skill to study the trail for signs of illicit activities and avoid low-hanging branches. "The rocks are pretty jagged on the tops of these hills," Fitzpatrick says, adding that's why the horses offer distinct advantages over their motorized counterparts. "Where you'd get a flat tire with an ATV or a regular jeep or a truck, your horse can get you back in there. It doesn't disturb the land."

It's also a lot stealthier. And the horse is, quite literally, an extra set of eyes and ears. "You'll see their ears perk and actually go towards whatever [they hear]," Fitzpatrick says. "They'll kind of give you a little heads up to things that are around you."

The northern border is regarded as a possible weak spot for terrorists. But most of the action focuses on stopping the trafficking of Canada's potent marijuana specialty, B-C Bud.

This is a change of pace for both Fitzpatrick and Kartchner. They're veterans of the busy Arizona border, where hardly an hour, much less a whole day, goes by without a chase. Up here, the mounted patrols have yet to make a single arrest. But Fitzpatrick insists, 'no arrests' doesn't mean 'no results.' "You gotta be patient. A lot of what we do here on the northern border is gather our intel up." Mostly, that means chatting with the locals -- something the agents find a lot easier to do when they're passing through on horseback.

From the top of Washington's Graphite Mountain, there's a clear view over Canada's Rock Creek Canyon. Agent Steve Kartchner says the mounted patrols are helping slow the smugglers' activities. "Now that we're here in this area, the smugglers aren't having such an easy time." But he also knows they're in a game where the rules are changing. "They're getting more desperate, so they're using more desperate measures. Our intelligence tells us that they're now starting to carry weapons and possibly protect their loads by that means."

So he swings back up in the saddle, being careful not to snag a leg on any of his own weapons. There's the semi-automatic handgun, and the shotgun he carries ? just in case they run into a grizzly bear instead of a terrorist.