You know you could find a place that sells gravel and rock by the pick up load, widen your driveway and put a fence right on the lot line and if that means that they would have to park partway on the grass they own then let them do just that or begin actually having a tow truck come tow their vehicles out. as to your other fencing If you must then move it so it is 3 to 4 inches to your side of the lot line( unless your city does not allow fencing to go that close to or right up to the lot line.