More experienced patrol agents. Radiation detection at ports of entry. New rules that require entrants to produce identification, where they once might have been just waved through.
A list of actions taken on the US southern border? Nope - the northern one. Over the last five years, while attention has centered on the flow of illegal immigrants from Mexico, the US has also tried to plug the holes in its leaky boundary with Canada as much as it can.
But given the northern border's length (4,000 miles), its remote terrain (forested wilderness), and the value of trade that travels between the two nations ($500 billion), sealing it remains a daunting task. Canada's recent arrest of alleged Islamist bomb plotters may be just a reminder that terrorists could penetrate the US from many directions.
"Threats posed from the northern border may not be any less than from [the] southwestern border," concludes a draft study of border vulnerabilities from the University of Southern California's Center for Risk and Economic Analysis of Terrorism Events.
Last Saturday, the Royal Canadian Mounted Police announced the arrest of 17 people who had allegedly plotted to explode fertilizer-based bombs at important sites in Canada.
Officials alleged that the group was a homegrown terrorist cell of Islamist extremists who had even trained together in a field north of Toronto.
Some of the detainees may also have had US connections. Several of the Canadians allegedly met with two US citizens from Georgia - Ehsanul Islam Sadequee and Syed Haris Ahmed - who are currently facing federal terrorism-related charges in the US.
US authorities charge that Sadequee, 19, and Ahmed, 21, made videos of the Capitol and other Washington sites to assess them as targets. The pair deny this, and so far there's no further evidence of a US connection to the alleged Canadian plot.
But the US border patrol says that it has still stepped up its vigilance, putting agents on the northern border on high alert and increasing inspections of incoming traffic.
"There is definitely a rampup of operations," Border Patrol Chief David Aguilar told reporters on Monday.
Still, the vast majority of border patrol agents are oriented toward the south, where the US last year intercepted more than one million people attempting to illegally enter the country.
About one thousand agents are spread out in a thin line along the north, as opposed to over ten thousand in the south. But that one thousand represents a three-fold increase over the number that guarded the 4,000-mile border with Canada in 2001.
And the northern agents tend to be more experienced. Typically, border patrol employees start on the southern border, and then, after a three- to five-year long learning process, are eligible for deployment to the north.
So enhancements on the border with Mexico will eventually pay off on the border with Canada, argue US officials.
"By augmenting and enhancing our capabilities on the southern border, that actually allows us to continue enhancing the northern border from the southern," said Mr. Aguilar at a press briefing on May 16.
The Canadian border also has a higher priority than the southern one when it comes to the placement of radiation detection devices, point out US officials. That is because the border patrol generally considers the risk of nuclear smuggling from possible Canadian terrorist cells greater than any corresponding threat from Mexico.
In general, the deployment of these devices has lagged behind schedule, notes a recent US GAO report. But 217 portal radiation detectors have now been installed at northern sites, notes the GAO - enough to scan 90 percent of the commercial trucks and 80 percent of private vehicles entering from Canada.
However, US land borders historically have been porous, and the boundary with Canada may be even more difficult to defend than the stretch of scrub, desert, and cities to the south.
The University of Southern California study, funded by the Department of Homeland Security and written by Niyazi Onur Bakir, judges the northern border "largely undefended." And it points out that the only confirmed attempts to cross illegally into the US for terrorism purposes have both occurred in the north.
In 1997, a Palestinian named Abu Maizar was charged with conspiracy to blow up a New York subway station after being caught trying to cross from Canada. And in a more celebrated recent case, the Algerian national Ahmed Ressam was arrested in Washington state after driving off a ferry from Canada in 1999. Ressam had bomb materials in his car, and had been planning to attack Los Angeles International Airport in the so-called Millennium plot.
Lax Canadian immigration policies are a potential terrorism problem for the US, complain some US experts. In particular, Quebec, which has its own immigration rules and is an easy entry point for French speakers from North Africa - such as Ahmed Ressam, the "Millennium Bomber" - may be a hole in the dike.
Geography is also a problem - the US-Canadian border contains some of the wildest land left in North America. Many of the Canadians and Americans who live near the Maine border are used to driving back and forth over unprotected checkpoints whenever they want.
New rules, currently scheduled to take effect in 2008, would require that all crossers produce a passport, or equivalent ID card. Congress is currently considering whether to delay implementation of this rule for 18 months, due to controversy over its possible effect on trade.
Finally, Indian tribal lands could be among the border's most vulnerable points. Those that sprawl near border crossings, such as the Akwesasne Reservation in New York, have long been havens for smuggling drugs and other contraband.