Place a 16-inch by 16-inch square of 1-inch sod or artificial turf upside down on a piece of newspaper. Place the flip-flops on top of the backing and trace them with a black marker.
Cut around the inside of the black lines with a utility knife, leaving you with 2-foot-shaped pieces of grass.
Place one grass cutout on top of one of the flip-flops. Cut a tab out of the tip of the sod to allow it to fit around the toe thong. Trim the edges of the grass as necessary to give it a good fit. Repeat with the other cutout and flip-flop.
Remove the grass cutouts from the flip-flop base. Apply a line of low-temperature hot glue all the way around the bottom of one of the cutouts. Press the cutout in place on the corresponding flip-flop. Repeat with the other cutout and flip-flop. Allow the glue to set before wearing.