Convincing the neighbours to give back some land
It can be a hard topic to bring up with neighbours if you think that your shared fencing may be laid incorrectly and that they may have inadvertently gotten some of your block on their side of the fence. This can lower your property value as well as limiting your usable space (both day to day and for any future renovations).
Here are some tips to help you investigate if this may be the case and how to rectify.
Research block plans
Dig out the old block details that you should have received when you moved into the house. It will have some measurements of each side of the block. This can help you to check if the sides of the block are the correct sizes. Sometimes it will be possible to gauge differences at this level, but at other times you may need a more sensitive measurement. Even a few centimetres over the length of a long block can add up a few square metres, which can impact both properties values and the space you have available for structures, such as sheds and garages.
Commission a land survey
If this does not help with your query, or if your investigations suggest a bigger problem, it's a good idea to call in a land surveyor. They can do accurate measurements of the land, accounting for issues such as slope. This can be a useful tool to approach your neighbour to help explain the issues that you have and to discuss moving the fence (or relaying a new fence) which allows you to get the land back within your boundaries.
Offer to pay for half
Even though you may be in the 'right' in terms of wanting to get your land back, it's generally accepted that the new surveying and relaying of fences will be split in cost between both parties, particularly if this is a misunderstanding which has continued for some time. The additional value that you gain in terms of your land area will generally far outweigh the cost of a small movement in the fence.
When dealing with land issues with your neighbours, it's a good idea to keep things as civil as possible. Using a third party, such as a land surveyor, can often add some much needed distance and perspective to matters relating to your neighbours. This can help preserve personal relationships and make it easier to manage any needed changes.