Sounds like the stomach pressups are one of the more popular stretches for herniated discs, anyone know of any other safe stretches?

Are these stretches safe for herniated discs?

On this one can you do both knees at the same time?
Knees to Chest
Stretches: Lower back and buttocks muscles.
Technique: Lying on your back, grasp the right knee with your hands and pull to your chest, stretching for 30 sec.
Grasp the left knee and pull to your chest ( thereby holding both knees) and hold for 30 sec.
Return the right knee to the ground, while holding the left knee, and stretch for 30 sec.
Tip: While holding each knee individually at your chest, pull the knee across your body to the opposite shoulder and hold for an additional 30 seconds. This stretches the piriformis muscle, a common source of lower back muscle pain.

Lower Trunk Rotation
Stretches: Lower back muscles
Technique: Assume position with knees up, feet together, and back flat.
Slowly rotate knees to one side and hold the stretch.
Move knees to the opposite side and stretch.
Tip: Placing your hands out to the side will help keep your back flat and improve your stretch.

Angry Cat Stretch
Stretches: Mid and lower back muscles
Technique: Assume the kneeling position Tuck your chin to chest, tighten your stomach muscles, and arch your back.
Relax the stretch by looking up, relaxing the stomach muscles, and dropping the arch.
Tip: Use padding under your knees if you have any knee pain.