Liberal Leader Peter Dutton and Opposition Indigenous Australians spokeswoman Jacinta Nampijinpa Price have yet to accept an invitation from mental health advocates to sign a respectful referendum pledge.

The pledge is a set of principles to encourage more civil and inclusive conversations about the Indigenous voice to parliament, that aim to reduce social and emotional harms ahead of the October 14 referendum.

It was developed by mental health experts, including the Australian Indigenous Psychologists Association and the Black Dog Institute, but Mr Dutton is yet to sign and was rallying people behind the 'no' vote when he spoke on Sydney radio station 2GB on Thursday.

"And there'll be a lot of Australians who don't even know that there's a referendum coming up and they'll engage in the last day or two when they're forced to, so those votes can shift and they can result in a 'yes' vote," he said.

"So we need to be very careful about there being no complacency."

Clinton Schultz, a Gamilaroi/Gomeroi psychologist and director of First Nations partnership and strategy at the Black Dog Institute, told AAP they had had a "great response" from Labor, the Greens and the crossbench, but it hadn't been so warm from the coalition.

Mr Dutton on Sunday flagged another referendum should the upcoming poll fail, one that would recognise Indigenous people but not enshrine a voice in the constitution.

However, academic Marcia Langton described the idea as pointless.

"There's no point in a second referendum because it's not what we want," Professor Langton told the National Press Club on Wednesday.

"We asked for recognition through a voice combining the symbolic and practical to give us both dignity and a sense of empowerment and responsibility in matters that affect us."

She said a 'yes' vote would deliver hope and healing through working together, but a 'no' vote would bind the country closely to a "broken status quo" that would continue the cycle of disadvantage and disempowerment.

"Don't imagine that there's another opportunity around the corner," Prof Langton said.

"Don't think your 'no' vote goes into a different pile marked 'next time'."

Professor Muriel Bamblett chairs the national body for First Nations children, SNAICC, and is also CEO of the Victorian Aboriginal Child Care Agency.

Prof Bamblett said if you involve Indigenous people in decisions that affect them you get better outcomes - and that the proof can be found in the statistics on reuniting children in out-of-home care with their families.

She said the agency she heads up reunites Indigenous children with their families at twice the rate of the state department.

"I'm very proud of the fact that we've got Aboriginal politicians, but they've been voted in to represent their electorate," Prof Bamblett said.

"I think it's important that we have Aboriginal people sitting at the table and being able to talk about what are really big issues for Aboriginal people on the ground.

"I don't want to wake up on the 15th of October to an Australia that doesn't recognise our voice and our need for a voice.

"Not having a voice constitutionally enshrined means that government can choose whether or not to even listen to Aboriginal people."

Rudi Maxwell - AAP