Border protection chief Angus Campbell has warned that stopping asylum seeker boats entirely will take "years, not months, of collective regional effort".
While there has been no successful boat arrival to Australia for five months, Lieutenant-General Campbell, the head of the government's Operation Sovereign Borders regime, said in a speech on Thursday night that his job was far from done.
At a dinner in Canberra for the Australian Strategic Policy Institute, General Campbell said that turning back boats, offshore processing and working with transit countries had meant "a very significant decline in the willingness of potential illegal immigrants to travel".
He added the usual post-monsoon surge had not happened.
But he said many asylum seekers were watching for relaxed policies. "At present, the great majority have decided to wait and see," he said.
"To modify a well-known and very apt phrase, 'The price of border security is eternal vigilance.' Unwavering determination to stay the course is now essential," he said.
"While the boats are stopping, with the flow very significantly diminished, the job isn't done. There will be surprises, disappointments and challenges ahead but we have come a long way."
He said the flow of asylum seekers into the region had "clearly slowed" and some had chosen to go home.
"That said, the benefits to date, while real, are modest. Substantially changing the irregular flow toward Australia and drawing down the pool of potential illegal immigrants in transit countries will require years, not months, of collective regional effort."
He said he had always been sceptical that boats could be stopped entirely, believing the flow would bottom out at one a week, unless Australian authorities began turning boats back.
General Campbell said that "irregular migration" was a fact of modern life, as "the ability of people to travel ... has never been greater".
"This trend shows no sign of abating. Much of that dynamic is of great benefit to our world and its people. But some criminals have made a living preying upon the vulnerable."
He said the conflict in Syria was a "push factor" that would drive refugees abroad.
He said the number of people crossing international borders had grown from about 77 million in 1960 to about 232 million in 2013, or just over 3 per cent of the world's population.
General Campbell also hinted he did not expect to head the new Australian Border Force, which will subsume Operation Sovereign Borders in July next year.
"I will look with interest to whomever might be appointed while pursuing other pathways in my life," he said. "I'm sure the government of the day will find a very talented official that can see the complexity, that can co-operate across institutional boundaries, and can change culture and perspective that might be required ... I wish that officer well."