Neighbours have an issue about their adjoining land parcels and have verbally agreed to sort it out in a certain way. One of them wants to make sure that the other is aware of the consequences and does not later ask to revert the agreed state of things.
What sort of paper do they need to sign, if any, to have the agreement binding? Deed of undertaking? Do the signatures need to be witnessed?
Example: Bob's land is uphill Rob's. Bob has done some earth moving which has changed the path of rain water drainage which makes Rob's land too wet where he doesn't want it to. Bob and Rob agree that Bob directs the water away from Rob's land completely. Rob is aware that it may cause his land dry out and promises not to complain about that. Bob wants it to be binding before putting effort into redirecting the drains.
Can that be recognised as a contract i.e. Rob's consideration is to refrain from making a certain type of complaints? I doubt this because Rob may never actually want to make those complaints, so there would be nothing moving from him.
Jurisdiction: any common law, though specifically interested in New Zealand.