Crown prosecutor Scott McColgan argued Tau's offending had a pattern of targeting young girls, luring them into his car and then sexually assaulting them.
He said a sentence of preventive detention may act as "some form of an incentive or a wake-up call".
"Preventive detention does not mean that he will never get out but unless and until you prove to us that those risks have gone or that they can be managed, we are not going to risk the community's well-being," Mr McColgan told the court.
In a November 2008 attack, Tau approached a 15-year-old girl who was in school uniform and listening to an iPod.
He told her he was a truancy officer, then told her to get into his car and he would take her home. Tau took her to her home, where he beat her and pushed
her down the stairs before sexually assaulting her.
Two other victims - attacked in 2007 and 2009 - were sexually assaulted in Tau's car after he approached them on the street.
One of the victims told the court that she was still having nightmares and suffering from back ache after being pushed down the stairs by Tau during the attack.
"You will never be able to comprehend the emotional trauma," she told the court.
She said she became numb and empty at the age of 16 and had nothing left to live for.
The woman also spoke of having her life put on hold six times as Tau's case was adjourned through the courts.
Her father also told the court of the pain Tau had caused his family.
"I have a deep, deep hatred for you personally that I have never felt for anyone else in my 48 years of life."
