The guards, who are paid from the school's operations budget, call principal Neil Watson or police if incidents occurred.
Watson couldn't be contacted for comment.
Cann said the guards "don't have too much legal authority".
"It's basically deterrence and to keep an eye on riff-raff really."
The guards were not hired as a result of the mass brawl at a recent under-15 rugby game between Otahuhu and Tangaroa colleges, he said.
Cann, who has been board chairman for five years and a board member for 20 years, said Otahuhu College was not alone in using security guards during the school day.
"Most schools have them these days. The private schools have had them for donkey's years.
"Its only been probably in the last five years that more smaller state schools have had them."
The Herald on Sunday contacted a dozen Auckland secondary schools from across the city, including state, integrated and private schools.
Of the five that responded — Auckland Grammar, Auckland Girls' Grammar, Rangitoto College, Macleans College and Aorere College — none used security guards during the school day.
Aorere principal Greg Pierce said he was also not aware of other Auckland schools hiring guards.
"And I was at Southern Cross Campus and Kelston Boys' before coming here and they didn't use security guards either."
Secondary Principals' Association of New Zealand president Sandy Pasley had not heard of guards being on duty during school hours at Auckland secondary schools.
Ministry head of sector enablement and support Katrina Casey said they did not record how many schools used security guards during school hours.
Day to day operation, including security, was the responsibility of the respective boards and school leaders, she said.
"Where schools and kura do use security guards, we would expect them to use accredited providers."