As an Olympic weightlifting coach, I like to vary the methods of loading the legs and posterior chain. The most important and predominantly used exercises are the front squat and back squat, with the front squat being a minimum of 3:1 to the back squat during program design.
An exercise that is a little more unorthodox to the weightlifter, but still an effective training protocol, is the sled push. The sled push allows for a variation in leg and posterior chain loading that reduces shear and compressive forces on the joints. Also, the risk of a soft tissue injury is reduced. Therefore, this exercise may be utilized with an athlete who is in a fatigued state, where the risk of injury is increased with the (frequency of the) more technical lifts.
As a chiropractor, I also prescribe the sled push as a substitute to any of the squat disciplines. I find that patients diagnosed with mild to moderate OA (Osteo Arthritis) of knees and hips, and some with AS (Ankylosing Spondylitis) respond well to the muscular loading provided with the sled push. This is done, once again, through the reduced shear and compressive forces placed on the joints. Another advantage with the sled push, especially with the older population suffering from OA, is the reduced technical instruction and experience required to perform this exercise.