The designation means Stanley Tippett could be jailed indefinitely.
Tippett was convicted two years ago on seven counts — including kidnapping, sexual assault and sexual interference — relating to the attack in August 2008.
A Peterborough judge made the ruling today, saying Tippett has shown a pattern of persistent, aggressive behaviour and a failure to control sexual impulses.
Judge Bruce Glass said only an indeterminate sentence can protect the community from Tippett, who has shown a pattern of escalating violent behaviour and a tendency to lie and manipulate people.
Glass said it is "wishful thinking" that Tippett could be treated.
"Mr. Tippett is a substantial risk to the community and will continue to be," the judge said.
Tippett claimed he offered safe passage to the drunken 12-year-old girl but was then carjacked by two armed men.
He was arrested just hours after the girl was found half-naked behind a school 70 kilometres from where she was abducted in Peterborough.