***If you have an injury don't do any of this without talking to your doctor. If you have pain, don't train. However, once the pain subsides and you get cleared:
Not sure if the other thread included planks (front, back, side), but I find they help my back a lot. I usually combine them with some other yoga type positions, controlling breathing and holding for as long as possible, then go to another position (Planks, up dog, down dog, yoga pushup, warrior, etc, start over and go through it again, etc.) No need for incense or nonsense, just breathe and try it, it works. The following website may help you get started
http://yogasite.com/postures If you can do it without any pain, rock climbing or bouldering helps too. Hanging from my hands and twisting my hips around helps alleviate the compression from vaulting, and all the supporting muscle groups get strong with lean muscle (no added bulk). However, falling can add more compression and hurt the lower back more, so keep that in mind.
Oh yeah, and don't take off under.
Good luck,
Tom