Romanian Dead Lifts=Awesome exercise for the glutes, hamstrings and a little in your lats.
Coaching cues: knees a little bent and shoulders blades pinched back as if you're squeezing a quarter in between them. As you lower the bar/dumbbell relax your arms and keep your shoulders back. Thinking about pushing your butt backwards and not lowering you back.
IF you feel this is your lower back it's most likely one of two things:
1) You're not pushing your butt back.
2) You're not keeping your shoulders back and most likely dropping your shoulders causing your back to round.
