Look into Westside Powerlifting or Metal Militia techniques.
If your lower back is lagging, your squatting ability will as well. Chain-suspended good mornings can help out in this regard.
Also, don't neglect volume. Bring your total set count for various squats during a workout to around 25 or so.
Vary your leg position. Close-stance squats hit the quads and glutes real well, and wides help with the hams and inner thighs.
If you have the money or access to a glute-ham machine or reverse hyper, take full advantage of them.
If you're having problems locking out, get 60-70 pounds of chains and/or some jump stretch bands. Even if you don't do specific dynamic effort days, you can still utilize them when doing heavy triples, doubles or singles.
Lots of people regurgitate the standard workouts you see in any gym or fitness center. Sometimes your body will respond with less conventional training exercises. Give zercher squats a try, dimel deads, box squats of various heights, CSGM's of various heights, overhead squats, GHR's, RH's, one leg squats, belt squats, incline squats, saftey bar squats, lateral roll squats, uneven squats, inverse curls, pull throughs, behind-the-back deadlifts... experiment and find what works for you!
