Perform your rows standing or sitting on a ball, keep your abs braced, head up, knees bent and shoulders back. Always keep the abs braced and the back flat; never round or hunch your shoulders. Do not lean back with the exercise. Proper abdominal contraction will counter any extension moment and protect the back while strengthening the abs.
Unfortunately the commercially made machines designed to strengthen the back actually place repetitive stresses on the spine and disks while encouraging hyperextension. The best way to achieve a strong back is to build strong abs and lumbar muscles with high endurance and coordination. The back was never designed to be strong; it was designed to have high muscular endurance and lots of help from the abdominal wall and hips.