If you're working to get your lower abs to pop, focus on hitting your entire core (including your abs, hips, lower back, and butt). Planks work great (side elbow, full, side). Vups are tough but they pay off big time. Leg lifts (figure 8s), bicycle crunches, flutter kicks, reverse crunches work good too.
If your lower back is a bit weak it'll make your gutt look bigger than it really is. Strengthen it hip-ups (aka bridge), locust pose (aka superman), and single leg floor lifts. Check out ab-workouts-guide.com for ideas to create a workout especially for you. I used to create my workout 20x10. Good luck and God Bless!