I have read many books about yoga and find that form differs sometime depending on the author. One thing that I am still confused about is the tightness in the hips when doing updog or cobra. Baron Baptiste says in updog to press tailbone down and roll buttocks in strong for a strong foundation. Then i will read where it says in another book to keep hips relaxed. For me, and i have a tempermental sacrum SI joint situation that will kick up pretty quick, the baron baptist way is more user friendly with my body. Could anyone comment? Thanks.

First off, a point of clarification: the "hips" is a vague term that usually refers to the bones of the pelvis and its joint connection with the femur of the leg. So technically you cannot tighten the hip joint, only the muscles surrounding the hip joint, usually the buttocks, internal and external rotators and the abductors abductors, and possibly the hamstrings.

Why would you engage these muscles surrounding the hips in cobra or up dog? To create hip extension to facilitate a deeper backbend and to keep the legs together and internally rotated. As you have discovered, when the hips do not come into extension in a backbend then the lumbar vertebrae and the SI joint take most of the pressure and stress of the extension. Engaging these muscles protects these joints and facilitates proper alignment of the pose.