Why on Earth would people do squats to failure on a regular basis (specially with a high rep count)?
Now, I'm assuming you are going to failure because you seek sarcoplasmic hyperthropy. In that case, if for some reasons your legs (and your body) respond better with working to failure, use the leg press (and go to failure with it) AFTER doing your squat workouts.
That should work better for you if you are experiencing back problems.
If there are two workouts you shouldn't be doing to failure, specially if your back is giving you problems, those two are the squats and dead lifts. And explosive lifts like cleans and snatches.
Now, if you are on the juice, then that changes the rules of the game (because of its recuperative, healing and anti-inflamatory properties.)
But even then, if you are having back problems, even with the juice, you should use better judgment and stop doing squats to failure.
If I were you, I would also consult a chiro and get some x-rays, or at least evaluate my external hip rotator, glute and iliopsas flexibility if I were you - a deficiency in either one of them will cause mobility problems on the bottom part of the squat. That's how I got my fucked up disks.
So don't be a fool and learn the hard way. Train intelligently.