we had a similar problem with the grass verge outside our house cars ,vans parking with 2 wheels on the grass 2 on the road.We put a couple of large rockery stones & painted them white a few of the neighbours have folowed suit as we all cut this grass to keep it tidy. it belongs to the council but only gets cut once a month by them.all was well for about a month until a driver ran over one of them she said she did not see it.she apoligised and said she was glad it was not a small child.as she was not paying attention to where she was going,very honest of her we thought.no more problems since.