I've had dogs all of my life and while I am most familiar with Labs, Rotties and Danes I think this will apply for any dog that has anxiety when in the tub.  I noticed my dogs seemed like they could not get comfortable due to the slippery surface of the tub.  One day I put a towel in the bottom the tub before I put my dog in.  She instantly relaxed like never before.  No nervous tremor, no standing on her toenails, no kidding!  She even sat down half way through and let me pick up her front paws to make sure they were clean.  Even the post bath cleanup was better.  Most of the fur she shed stuck to the towel which I wrung out and put immediately into the washer.  Done deal pickle!  A few baths later I decided to try using those dollar store cloth bath gloves (for humans) to see if it would help me get more of an overall clean rather than the traditional clump of too much shampoo on one side while missing half a dog on the other.  It worked like a charm.  Nice overall lather.  Diminished gross out factor in the uh..hind quarters and wonder of wonders my dog acted like she thought she was getting a treatment at the spa rather than a dose of water torture.  When we're done I add the gloves to the wash with the towel (high tech improvised doggie traction device) from the bottom of the tub and the one (or four) I used to dry her off.  We finish in record time and celebrate our new found genius with a cookie (for me) and biscuit (for her).  Cheers and happy tubby times be yours!