Dr. Squat Strap
Fred Hatfield, otherwise known as "Dr. Squat" once set the world record for squat weight at a whopping 1,014lbs. He credited his success to an exercise called the Hatfield Back Raise, a brutal exercise that uses a harness and the glute/ham raise to significantly impact erector muscles. Since the HFBR keeps the fine fully supported, it's become a favorite of lifters with lumbar disc injuries.
The Dr. Squat Strap can be used for those and much more, from good mornings to pull-throughs, RDLs, zerchers, and sled drags.