You need a barbell, a belt, a carabineer, and something to secure one end of the barbell, such as the Landmine device. You can also just jam one end of the barbell into a corner and put a heavy dumbbell on top of it. The setup is very similar to old school T-bar rows, only you're squatting instead of rowing.
With one end of a barbell secured down, attach a belt to the other end of the barbell and start squatting. Use 25-pound plates for a greater range of motion.
This setup allows you to sit back further and maintain a more upright torso. Moreover, the arc of the barbell is such that you're pushing back slightly on each rep, which smokes the quads.