Officers at the National K9 Centre in Majura say a man's best friend is also the best detector of hidden drugs, money and explosives.

But one in three of the hand-picked Labradors housed in Majura never become fluffy detectives.

AFP canine trainer Jayson Mesman said the selection process was akin to that of sports stars.

"Customs breed between 200 and 400 dogs a year. We only look at about 50 of those and about 70 per cent pass," he said.

"It's like athletes, everyone might be pretty fast but you're going to have your standout players and champions."

Those who don't make the cut - or more bluntly, get fired - either return to the border force where they may be offered to other agencies to become detector dogs or get adopted out to members of the public.

So just how hard is it for a dog to become a four-legged Sherlock?

The AFP opened the sniffer dog facility at its Majura complex in 2007. Labradors are sourced from a number of places but mainly the border force, where they are bred and fostered out for about a year.

Many puppies are disqualified before even leaving the border force, as only those of the most sound temperament and intelligence, and with the keenest hunting instincts, are sent to Majura at 14 months old. They then undergo a 13-16-week intensive training course in detecting hidden drugs, cash, firearms, and bombs.

Once (and if) the fluffy agents graduate, they're assigned a handler and sent to airports, seaports, cargo depots and international mail centres around the country. State and territory police also draw on them for search warrants and events such as music festivals.

But the tests are tough when the stakes are as high as public protection.

Mr Mesman pointed to a whiteboard outside a simulated house, one of three scenarios used for the dogs' training. The whiteboard listed names of the 14 trainees in the current 13-week course. By week three, two had already been laid off.

One of the biggest challenges for both police and their dogs is the myriad of scents the canines are required to detect. Officers are constantly on the lookout for new drugs on the market and updates in technology, and the dogs must be trained to sniff out each new substance.

"Any trend that is happening, we are either ahead of it or not far behind," Mr Mesman said.

"If there is a new drug coming in from overseas or domestically as a threat, we are working on that, and I guess that's the power of the whole of the AFP, because we work across all the different areas to collate that information."

Dogs are not addicted to drugs, despite what many people think, but to the game of hide-and-seek that underpins their training. They are taught to sit when they recognise the smell of the odour being tested, which had been fermented on a hidden toy. Each stage of the game becomes more difficult as trainers hide drugs among obstacles such as long grass or confusing household items. If the dog walks past a scent, they're out.

Mr Mesman said the tough standard was why a third of the dogs don't graduate, and why those who do never rarely it wrong in the real world.

However, the effectiveness of sniffer dogs has been called into question on several occasions, including when NSW figures revealed the proportion of searches where no drugs are found remained stubbornly high.

But handler and Senior Constable Craig Manning said he found that only inexperienced dogs made mistakes - and they were quick to learn from them.

"The dogs are definitely capable of some amazing things, and the more experience they have the better they are," Mr Manning said.

"With drugs, the best dogs will find smaller amounts where as the majority of dogs will find bigger amounts. But the majority of times they should distinguish what they are and aren't looking for."