The BoxxyBall boundary kit comes with 4 x nails (4 x grass & 4 x sand) and 4 x bungee cords.
Unwind the black boundary webbing from plastic spool, and lightly secure nails to hold metal corner rings in position until the boundary is established.
Return to each corner, remove the nail and attach one end of the bungee cord to the metal corner ring. Slightly stretch the bungee, attach the other end to a nail, and hammer into position. The boundary should be held securely, flat on the ground and able to stretch if someone trips over the it.