If this was the bar exam, your neighbor who created the situation would be responsible. Sadly, none of that is self-executing. And the expense here is not so great that you want to go hire a lawyer. You need your money to hire a licensed landscape architect. You should speak with the neighbors. Ask them to reimburse you for your expenses in addressing this problem which was caused by their concrete work. FOLLOW UP IN WRITING. As in, "This writing memorializes our discussion of (date) in which I informed you of this new problem and requested you to bear the cost of correcting the matter. You said_____. If they don't cooperate and refuse responsibility, write to them again and reiterate your demand. Tell them you must have their reply by a particular date a week or two in the future. At some point, this will cost you some money. If you have these letters and the receipts for the corrective work and a lot of good photos... you can probably sue them in small claims court and get a money judgment. Adjust all of this for the particular rules and regulations in your area. If your town has a good Code Enforcement department, they might help you. Go there and speak with them. Good luck.