What should I do about my grumpy butthead of a neighbor who wont mow part of his lawn?

My neighbor is being a dingus and not mowing a portion of his lawn near our house... Ideas on how to address this? We've already talked to him last spring and he's back at it. Backstory: We moved into our home about a year ago, and upon move-in, the previous house owners informed us that they were... show more My neighbor is being a dingus and not mowing a portion of his lawn near our house... Ideas on how to address this? We've already talked to him last spring and he's back at it.

Backstory: We moved into our home about a year ago, and upon move-in, the previous house owners informed us that they were accidentally mowing a huge chunk of the neighbor's lawn for a while because it appeared to be the property of our (now) home. Once they put the house up for sale though, they had a city surveyor confirm that it is actually the lawn of the neighbors. At that time, they informed the neighbors of this and had lawn magnets put in to mark the property.... so they are well aware.

However, since moving in, the neighbor has not mowed that section of their lawn. It's about 5 feet wide and the length of their entire property. It's on the outside of our new fence which slopes down to their lawn.

When we moved in, he made a very passive comment about how he thought that was our lawn after we didn't mow it once (lies... obviously he had no idea we talked to the previous homeowners). It's not a major issue, but the principle of it is super annoying and it seems really petty and childish to not mow a section of your own damn lawn....
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