Back rehab starts with activation of the deep spinal musculature, the multifidi and intertransversarii. They respond very well to isometric exercises, specifically, co-contraction of the abs and gluteus.... picture yourself lying in bed and squeezing your glutes and gently contracting your abdominals without moving.
If this goes well for two weeks it means these STATIC stabilizers are getting stronger, and this is an essential first step.
Then, and only then, begin isokinetics (exercises with movements). Doing these with a five second negative and five second positive contraction for 6-8 res will give you at least a full minute of time under tension, and continue to activate the static stabilizers, and also bring in the prime movers to contribute neurologically. Then, add heavier loaded exercises, deadlifts, squats, etc as tolerated, but keep up this basic ritual of training as a part of your warm up.
I works extremely well with my patients, and they get better and stay better. Be smart and train for life!