In a bizarre twist, if he lodges an appeal, he will be fighting a decision made by his own employer.
It has now emerged that Mr Walmsley works for the city council's IT department on a fixed-term contract.
Council city planning and design manager Warren Ulusele said he was waiting to see whether the appeal was filed.
"Until then, we can't take any action.
"But as things stand, the existing structure is not permitted and on that basis the council's intention is to seek removal," he said.
The Aitchisons claimed the fence immediately slashed their apartment's value by $900,000 and the retired couple spent $100,000 in the Environment Court fighting for the removal of the fence.
They hoped the council would compensate them for their legal bills - but they were not confident.
Mr Ulusele said the council had an agreement to share costs with the Aitchisons but they "chose not to [do so]".
The council could not stop Mr Walmsley from building the fence.
"We did not want this to go ahead but we couldn't legally stop him," he said.
"The court's decision does have implications for the development of the city.
"Any future development could potentially go through a more stringent and costly and longer timeframe process as a result of this decision," he said.
Mr Walmsley had previously attempted to build a fence, but he failed to get consent.
Until yesterday, Mr Ulusele did not know Mr Walmsley worked for the council.
Mr Walmsley could not be reached for comment.