Demetriou said the arrests last weekend over alleged match-fixing in the Victorian Premier League had ended any illusions that Australian sport was immune from such problems.
"There were those who were cynical about the Australian Crime Commission report in February ... and the rapid response made by the AFL Commission and the executive to close down any loopholes," Demetriou said.
"But events of the past week have certainly put paid to any cynicism.
"Ten years ago, such thinking was not on our radar.
"Rest assured, our integrity unit has all the resources possible to ensure we apply the best techniques to protect the purity of our game."
Speaking at an AFL function before Friday night's epic preliminary final at the MCG, Demetriou also staunchly defended the AFL in the wake of the Essendon supplements scandal.
Late last month, the AFL threw Essendon out of the finals and suspended coach James Hird among other penalties.
The Australian Sports Anti-Doping Authority (ASADA) investigation into the club is ongoing, with speculation this week that heavy penalties were on the way.
"I know 2013 has had its issues, but I'm proud that the AFL has been transparent in every part of the process to ensure our game is played with the greatest integrity, to the values that define sport," Demetriou said.
"We must all remain vigilant and active in a world in which too often the beautiful nature of sport is being exploited by the unscrupulous and selfish."
Demetriou made a point of singling out two guests - ASADA chief executive Aurora Andruska and Victorian police deputy commissioner Graham Ashton.
"The AFL is grateful for the work that ASADA has done with us this year in difficult circumstances," Demetriou said.
"Our relationship with the Victorian Police has always been close and I'm hopeful we can have an even closer relationship to ensure any intelligence is easily exchanged between us when relevant to the integrity that drives our game."
Demetriou is about to mark his 10th anniversary as AFL chief executive and said his brief when he started was simple - "taking the game to a better place".
"On balance, I'm sure, through this collegiate effort our game is in a better place than it was in 2003," he added.
