Beating the Squat Butt Wink
Squat Depth is an interesting subject. People are either being ragged on for going too heavy with quater depth squats or being criticized even further for dropping plates and going ass to grass.
Going full depth may have its benefits, however if you don't have adequate hip range of movement you will experienced the dreaded butt-wink! What this refers to is the movement at the end range of a squat where you run out of hip flexibility causing your lower back to flex and then extend. As you progress with heavier and heavier squats this will place greater pressure on your lower back discs prediposing you to injury.
The following article has an interesting discussion on how to identify if you have a butt-wink and how to correct it and how to ensure that you squat form is on point.