Best way to get your lower abs to show is to get your body fat down. Also, focus on exercises that hit your lower back and hips. If any of the areas is weak your lower belly might look a bit bigger than it actually is.
I built this exercise (Core Blast) from workouts I found here and at ab-workouts-guide.com. It's tailored to hit all of the areas of your core (abs, hips, lower back, and butt).
Good luck and God Bless!