If you reach an agreement put it in writing and both of the parties should date and sign it.
You should give your neighbour a Notice to Fence by either registered mail or personal delivery. The Notice should state;
If after 28 days, you have not received a response to your Notice to Fence, or you receive a response objecting to the Notice to Fence, the matter may need to be decided by the Small Claims Tribunal before you can proceed with the fencing.
If you go ahead and build the fence without the consent of your neighbour or the Small Claims Tribunal, you will be required to pay the entire cost of the fence and/or remove the fence.
The Tribunal Referee can decide all issues relating to the fence.
If you are putting in a swimming pool and have to change the fence between you and your neighbour in order to meet safety standards, then, as the pool owner, you will be required to pay all the costs involved.