Gravity and joy-riding kids can make swinging gates sag over time. To square up a droopy gate, turn an eye screw into the gate frame near the upper hinge. Fasten a length of steel cable to the screw with a U-bolt clip. Place another eye screw diagonally across at the lower corner of the gate and fasten a second length of cable. Connect the two cable ends with a small turnbuckle. Then rotate the turnbuckle shackle with a screwdriver to draw the two cables together until the gate is square.