I use the black plastic edge on the lawn side, sunk so the rolled top is right above ground level so that it is hidden by the grass but restricts lawn roots. Then on the bed side of the strip I lay bricks or pavers so that their top is just above the level of the rolled edge. That way DH can run the mower wheels on the brick and the edging gets done as part of the mowing. Just do the direction so that the clippings don't get thrown into the bed.