Any ideas? I know it's the lower two that aren't developed, but nothing I seem to do can get them to consistently stay.

I've done tons of leg raises, suspended leg raises, weighted lock outs... nothing seems to work.

Lose the body fat covering them.

Here's what you do...walk to the corner store and buy a 12 pack of beer. Drink 4 of them as you walk home, and when you get home, you have an 8 pack!

Seriously, if you want to try something different, and very painful and difficult. This, IMO, is the best ab workout.

Lie on your back, on the floor, or on a mat at the gym. Keep a clock where you can see it. Then lift both legs off the floor 6 inches about the ground, legs straight, knees just slightly bent, then hold that position for 30 seconds. Do not let your feet touch the floor. Then raise them both to 12 inches off the floor for 30 seconds. Then go back down to 6 inches. Keep doing this for 3-4 minutes. The whole time your feet must never tough the floor for 'relief' or a rest.

After 2 minutes you are burning and sweating..after 3 minutes of this the only way you can keep going is to think of your happy place.

It's the toughest ab workout I've ever done, and will also toughen you up a bit.