Good mornings are a great exercise, as are SLDLs/RDLs, and beltless work on squats and deadlifts.......Remember to think in terms of your core and not just low back and do plenty of ab work as you are building your lower back. Personally, I do all my ab work weighted. Don't let anyone tell you that weighted ab work will make you fat, thick, blocky, or bulky. Overeating is the sole cause of all those things.