If you're already lean and it's muscle-related, try doing vacuums. Also, try to do them while contracting and pulling up on your transversus pelvic floor.
Have your tried leg raises?....also look into differen't types of lower ab excercises on some of the sites listed on this page where you focus on the ab are by more leg mobility...Diet is also essential like love handles this is an area that fat tends to love to go to.....Learn about avoiding mixing certain foods together that produce a lot of insulin...what happens is when your body produces an abundance of insulin especially after a meal it tends to store in the lower abdomen and thigh area (hence the pear shape so people have.)
Look doing a million crunches or whatever exercise will not make it go away. It is excess bodyfat. No, you cannot spot reduce. Lowering your overall bodyfat is the only way to make it go away.
Continue to train hard and staying on the strict diet is the only way!