Since your neighbors already have access rights to use the drive, it is unlikely they are doing this to gain any sort of rights. They may be trying to please you. Try talking to them and ask them why they had their hired help cut the grass again. Perhaps the hired help is just fulfilling the orders given to them by your neighbor, reguardless of whether or not the grass has been already cut 3 days prior. They may be "just doing what their paid to do". It seems obvious the grass does not need to be cut that often. Try talking to your neighbor, and come to an agreement on who will cut the grass. You may be the lucky one, and let the neighbor pay to have someone cut the grass. Its one thing less you have to do. Take a candid approach, and go talk to your neighbor, and remember not to blow things out of proportion. Give it a shot. Good luck.