Anything that will kill grass at that frontier will leach into your neighbor's lawn. Once you make him an enemy, life will change. Continuous 4" high plastic or metal barriers are what works. It comes in rolls 25 ft. or so. It it's corregated, that means it's made of less strong material that will degenerate more quickly. It needs to be sunk about 3" deep and still have 1 or 2 inches sticking out of the ground. Otherwise, the grass will go under or over or both. Anything that has seams, like a row of bricks, will have grass growing in-between them in no time flat and require hand pulling. Aluminum is better than plastic if your ground freezes because the plastic will be extruded a little with each freeze/thaw cycle. Nothing is cheap or easy.