Wilson will have to adhere to 17 conditions that strictly curtail where he can go and who he can associate with.
He will be banned from contacting his victims, must seek permission before inviting females into his house, and cannot have contact with anyone under 16 without permission and supervision.
The board did not impose a curfew but stipulated that Wilson must not leave the Wanganui district or move house without written approval.
He will also be banned from owning a car, joining groups or clubs and using the internet without permission.
The Department of Corrections today confirmed Wilson would be one of fewer than 10 parolees who must be accompanied at all times.
But Wilson's lawyer, Andrew McKenzie, said he would challenge the board's decision and the department's measures.
"He's essentially being put on house arrest. We say that's beyond their powers, so that will be matter of course for the courts to weigh up," he said.
"We don't accept that there is a condition that he has to be tracked or followed by any people. And the GPS condition is just a waste of technology because there are no issues like a curfew.
"If there was such a condition then I think they needed to be honest and up-front with the Parole Board and Wilson and say, 'This is what we're proposing' - and they haven't done that, so we would doubt that would hold up legally."
There were "no appeal rights as such" when it came to parole decisions, but Mr McKenzie said a judicial review could be one option.
Another option was to apply to the High Court "on the basis that you are being unjustifiably detained - which is really that there are unjustified restrictions on your liberty".
"That's probably the quick vehicle - but it may well be that there's a bit of both, just to make sure the arguments are all before the judge," Mr McKenzie said.
"There will definitely be a legal challenge. The issue in the next days is how that should occur, when that should occur - because it may well be that some legal challenges are only available once you are actually under detention."
Corrections Department chief executive Ray Smith said the conditions would be the strictest ever imposed on a parolee.
"We've done everything we can think of to reassure people that we're taking this really seriously."
There were fewer than 10 offenders who were constantly monitored and accompanied at all times.
"The kind of freedoms that most people experience when they are released from prison will not be experienced by him, and that's to do with his offending history, his inability to participate in any form of rehabilitation during his 18 years in prison," Mr Smith said.
"He has to be released legally - I have no ability to hold him in prison. And so what we've got is a very restrictive regime that allows him to live outside the prison, but I think in a way that both the police and Corrections Department can exercise a good degree of control.
"He can live a quiet life on prison grounds and he will be able to leave the grounds accompanied by others - that's the kind of plan that's been set up."
Corrections had begun to introduce GPS tracking of high-risk offenders this month, and Wilson would be among the first the new technology would be used on.
The technology was useful because it allowed Corrections to set up "exclusion zones" that set off alarms if people went where they were not supposed to.
"You can see their patterns of where they spend their time and how they move around, so it gives you a lot more information about offenders that you're worried about, that you can't see all the time."
