Plastic snap edging is the way to go. just drive in 8 in landscape
spikes to secure these retainers then backfill with topsoil or gravel
right over them. the grass will also root straight thru the openings.
http://www.snapedgeusa.com/ You can also use plastic brick stop
edging like this:
http://www.brickstopcorporation.com/...ic_edging.html