I had the same thing the last couple years. A neighbor on one side had a guy who would always mow 2'-3' into my yard (at about 1.5") so I finally called him and explained the problem and it was solved. This year i mow their lawn so problem is really solved!
The other side was mowed by another company who insisted on using their 60 Lazer for everything and if their landscaping was 24" from the property line they would still go around it cutting into everyones yards. They also NEVER made a pass around the property and wherever they turned around is where they left it. The line looked like a scallop and would sometimes be up to 4' into my yard. That company was bought out and these guys do a little better but since I started a lawn service they maybe switching to me anyway so that problem will be solved also.