"As we all know, even the closest relationship needs care, nurturing and constant attention," MacKay told a conference commemorating the 10th anniversary of 9-11.
"Since 2001 we've been paying particular attention to the concerns, challenges and the expectations of you, our closest friends and allies."
As Canada and the U.S. have worked side by side around the world post-911 _ particularly in Afghanistan and more recently, in Libya _ the two countries have been working hard "to strengthen our security partnership here at home," he said.
Discussions on a border perimeter security agreement are ongoing, he added, and are "very productive." An announcement on the so-called Beyond the Border initiatives is expected sometime this fall.
"Beyond Borders, I believe, will help enhance our abilities to address threats early by improving the screening of persons and the cargo that is entering North America, while not unduly thickening the border," MacKay said.
"I would far rather see a thicker perimeter than a thicker border between our countries."
The initiatives will also enhance cross-border law enforcement, he said.
"At the same time, it will facilitate trade, movement, the creation of jobs and economic growth throughout the continent," MacKay added.
The conference, hosted by the non-profit Foreign Policy Association, was held in the city hardest hit by the terrorist attacks 10 years ago, and dealing on Friday with heightened security measures as authorities investigated a credible al-Qaida threat timed to this weekend's anniversary.
More than 3,000 people perished when terrorists flew jetliners into the World Trade Center towers in New York and the Pentagon in Washington amid a shocking sequence of events that stunned the world and changed the course of contemporary geo-politics.
MacKay's visit came a day before his boss is scheduled to arrive. Prime Minister Stephen Harper is travelling to New York this weekend to take part in commemoration ceremonies.
Harper will join a public memorial service on Sunday in lower Manhattan. "On this day, we will pay tribute to Canadians, Americans and all those who lost their lives nearly 10 years ago in these heinous attacks," Harper said in a statement Friday.
"As we pay tribute to the victims and their loved ones, we also honour members of the military, law enforcement and intelligence personnel who continue to fight on the front lines against all forms of terrorism."
The evening before, the prime minister will meet privately with the families of Canadians killed in the attacks. Harper will show his support for those affected by "the senseless and tragic attacks," said the statement issued by the prime minister's office.
Canadians have been celebrated in the United States this week for their roles in helping Americans endure that terrible day 10 years ago, and those that followed.
The Newfoundland town of Gander received an international resiliency award at a day-long event in Washington for opening its heart, and its homes, to thousands of people stranded there after flights were grounded on 9-11.
The outpouring of American gratitude and affection for Canada on the anniversary is an antidote to the tensions that developed in the relationship after the 2001 attacks.
American citizens and legislators alike believed for years that the terrorists had entered the U.S. through Canada, a myth that still persists.
They were critical of Canadian immigration policies and feared Canada's border was a porous one. Border security measures were beefed up to such an extent that exporters on both sides of the boundary complained that trade and commerce was significantly hindered.
MacKay didn't touch on those tensions in his speech, focusing instead on the closeness of the friendship and the efforts made, post-9-11, to work with Americans to secure the border.
"Friends, ours is indeed a unique relationship, and I believe a critical relationship, one that we share more than the continent of North America," he said.
"We share values, perspectives, history, a common desire to live in a peaceful and prosperous world where freedom and human rights are protected, and in fact revered."