If you and your neighbour agree on the work and the cost-sharing, you do not have to follow the procedure under the Fences Act. However, even if you do not follow the procedure, it is wise to make a written agreement, signed by both of you.
It should state clearly what work is to be done, what materials will be used, what quotes have been accepted, and how the cost will be shared.
Attach copies of quotes for all work. A clear, signed agreement should spell out what was agreed to - without it you could still end up in court.
What if we can’t agree?
If you can’t agree, try mediation first. This can be cheaper and quicker than court,
Source:
https://lsc.sa.gov.au/resources.pdf
FENCESAND THE LAW - Legal Services Commission of S.A.