BB Hacks 4X6 to 9 reps. Think of them as reverse DL's, but with a little more leg action and less strain on the lower back (no bending forward, keeping the back straight).
GoodMornings 4X6-9 reps. Slight bend to the knees and a arched/straight back.
Knee up's (elbows resting on dipping bar) Weight attached to ankles. 2 X 8-10 reps. Ab work can be important when doing heavier leg/lower back training. Need that muscle balance between both.
Good Luck