Neighbor Dug A Trench Across My Yard

For a bit of context: I live in a small neighborhood and my house has a neighboring house just a little over 5 ft away. This neighbor has a violent past and I've already asked him numerous times to stop. Our backyards have a natural swale.

My neighbor had decided one day he was going to completely regrade his yard which causes water to now build up on my side of the house (there is flooding happening to the neighbor on his other side) and has decides to dig a trench to put in plastic tubing through the swale.

While we got him to take some of his stuff out, he hasn't removed all of it and I've been buying dirt and sand to refill and form the swale, but I have a bad back so I've been struggling to repair it. Though he just undos the work I did so it feels futile.

We call the police once since he was actively trespassing at midnight during the week a bit ago and the cop lied about where the property lines were at saying he was digging on city property (we had since gotten confirmation through a surveyor and checked with the city that what he has been doing is on our property).

I don't know what to do or if I'm just screwed. My wife and I are actively trying to sell our house, but are fearful it won't sell do to this neighbor.