I’m currently in discussions with my rear neighbour about replacing our fence and the retaining wall it stands on. This neighbour's property sits higher than us based on the slope of the street/land and for the past few years, the retaining wall has been breaking away and subsequently damaging the fence. The 2 main reasons for this damage is that they had a very large gum tree on their property right on the fence line and the fact that they are using the colourbond fence as retaining wall to hold up their yard, rather than a solid retaining wall in their yard. My husband and I worked with them to remove the gum tree which was on their property and paid half for the removal. This was over a year ago. We agreed not replace the retaining wall and fence straight away due to the possibility that we were looking to either renovate or extend or knockdown and rebuild. We ended up knocking down and rebuilding and are getting close to completion. We recently approached them re the fence and retaining wall and presented them with our quotes,, etc.... This did not go very well! While they seemed willing to contribute to the fence, they appear not keen to contribute to the retaining wall. Without a stable retaining wall, we can not keep their yard from coming into ours and we also cannot replace the fence. I would like to know where I stand under property law and what possible rights I have given that it’s their tree and yard which has been destroying the retaining wall for all these years! Is it their responsibility to retain their land?