London, England –  World Anti-Doping Agency president John Fahey hopes the most tested Olympics in history will keep them "as free from doping as is possible." But even if the number of cheaters caught here remains small, there's nothing to say it won't go up in the future.

New and better tests, cooperation from pharmaceutical companies and the so- called Athlete Biological Passport are some of the new generation ways dopers are being caught.

Samples collected at the Olympics are kept for eight years, a long time to sweat not getting caught if you're a cheat.

"If someone thinks they're home free in 15 days time from some form of cheating here in London, they should hold their breath for at least eight years because the odds are they can be picked up at a later point in time," said Fahey.

He spoke Wednesday at WADA's traditional pre-Olympics press conference and on the heels of news that retesting of samples from the 2004 Athens Olympics may have yielded some positives.

In the six months leading up to July 19, at least 107 athletes were banned from competing in the London Olympics based on at least 71,649 tests. Of course, not all of the athletes would have qualified for competition through their national organizing committees.

"But had that been their ambition, I'm pleased to say that they are not with us in London," said Fahey.

He said it will be more difficult to cheat in London than at any other Olympics, not surprising considering the evolution of testing methods.

The IOC and London organizers are in charge of doping tests, which are given to the top five finishers in each event. Test are also done randomly and some are given based on intelligence gathered by various organizations -- WADA isn't keen on speaking about the latter method, preferring to keep the details as secret as possible.

Another method to catch cheats being used by at least six sports, including track and field and swimming, is the Athlete Biological Passport, which uses a number of tests over time to create data for a specific athlete. The theory is that tracing an athlete's timeline with biomarkers will make it harder to cheat undetected.

The IAAF, track and field's governing body, announced Wednesday that six athletes have been sanctioned through its biological passport program, and three new cases of doping were confirmed through retesting.

The IAAF said the group of six athletes was marked as suspicious, and was regularly targeted for in- and out-of-competition tests. Their blood profiles were then flagged as abnormal and reviewed by a panel of experts.

The biological passport also helped generate leads for the three athletes whose samples were re-tested.

Two of the athletes, Ukrainians Nataliya Tobias and Antonina Yefremova, had blood samples taken at last year's world championships that showed irregular levels of testosterone. That triggered a retesting of urine samples they gave during a pre-worlds training camp, and those samples showed the use of synthetic testosterone. Urine samples taken at worlds a week later were negative. Biological passport measurements also led to the detection of growth hormone in a re-testing of a sample from Bulgarian Inna Eftimova.

But it's not an easy tool to use, Fahey said, because each sample costs money.

"It's just another weapon in the fight," he said.

As is a new test for human growth hormone, which is in place for the London Games. The new HGH test is based on biomarkers, unlike the older test, which relies on detecting a concentration of the synthetic hormone in blood samples.

The biomarkers test could detect other signs of synthetic HGH use. Its use was approved in the last several weeks after being researched and reviewed for nearly 13 years.

"It's something that underwent a really strong period of scrutiny, but it's now in place," said David Howman, director general of WADA.

Howman said the two tests are complementary, not separate, and both are being used here.

Having a window to retest athlete samples allowed the IOC to turn up positive tests for CERA -- a new form of blood-booster EPO -- after the Beijing Games four years ago.

Because CERA went on the market six or seven weeks before the 2004 Olympics, the lab in Beijing wasn't trained in time to pick it up. The IOC reanalyzed samples months later and caught five athletes who had used it, including runner Rashid Ramzi of Bahrain, the winner of the men's 1,500-meter race.

Under a proposed rule, athletes like Ramzi would be automatically banned from competition in the next Olympics. The "Osaka Rule" is still being discussed even after its use was thrown out in the case of U.S. sprinter LaShawn Merritt, who won an appeal to defend his 400-meter title after receiving a ban for taking the penis enlargement product ExtenZe.

Fahey doesn't see a lifetime ban for doping ever being a possibility, but he hopes all the new methods of detection will make athletes think twice, even if it's a pipe dream to think there will be a drug-free Olympics. He's especially keen on the eight-year window to re-test.

Said Fahey: "To me, there is nothing better in the way of a deterrent than to be able to say to athletes that, 'Here you are. You thought you were free but eight years later you've been picked up. So don't be stupid. Avoid it.'"