Cut them into two sets of varying lengths (6', 2' & 2 @ 4') and stick in the ground capital side up and use them to stage container plantings on. I'd look for shallow, dished containers that match in scale width-wise and make sure to use a lot of plants that will drape and cascade over the side. I'd group 3 of varying lengths together and use the 4th one individually elsewhere - things always look better in uneven numbers :-))

As an entrance to a special section of your garden