Astavakrasana (Eight-Angle Pose)
Even so, your leg may still slide when you let go with your hand, unless you grip with your inner knee more powerfully than with the outer. Try gripping with your outer knee, let go with your hand, and see what happens.
Then reposition your leg if necessary, stretch the foot as described, grip with your inner knee, release the left hand, and observe the differences.
This kind of experimentation is crucial in practicing yoga. If you've watched children play with a new toy, you've seen them try to do all sorts of things with it, quite often having nothing to do with its intended purpose. Their play is tied into their sense of curiosity.
For the student of yoga, a similar willingness to play with first this movement, then that, coupled with the more mature process of observing the effects of your actions, will teach you a lot. When I first began to study with B.K.S. Iyengar, I heard that he used to practice eight to 10 hours a day. This was inconceivable to me, not only physically, but from a mental standpoint. How do you stay interested for that long?
After nearly 30 years of practice, I think I now understand how this is possible. Your practice—or anything else—stays interesting as long as you are experiencing it as fresh and new in every moment.
I've watched my grandchildren play with the box a toy came in for a much longer time than with the toy itself. The simplicity of the box invites them to be spontaneous and allows them to explore the many possibilities that arise in their minds. When you approach an asana with a similar attitude of inquisitiveness and playfulness, following the natural curiosity of your own mind, it's amazing how many possibilities can arise. I have done Adho Mukha Svanasana literally thousands of times, and yet each time (all right, most times) I find it interesting, mentally stimulating, fun. What if I turn my hands out? What if I turn them in? Widen them? Narrow them? On and on it goes. A lot of times I have to quit playing with the asanas because I've run out of time, not because I'm tired or bored.
As you turn your attention back to Eka Hasta Bhujasana, bear in mind that your willingness to play with the pose may be more important than whether or not you can "do" it.
To continue exploring the pose, keep lengthening the arch of your right foot, press your inner right knee firmly against your upper right arm, and release your right ankle with your left hand. Place your left hand on the floor about six inches outside and slightly forward of your left hip. Roll your left thigh inward, and intensify the grounding of your left femur by broadening the ball of your left foot. Take a breath and, with an exhalation, press your palms and lift your left leg and both buttocks from the floor.
To access the full strength of your arms and wrists, press the mound of the thumb powerfully into the floor. Keep your left leg straight and parallel to the floor, and make sure you keep rolling your thigh inward so that the kneecap and the toes face the ceiling rather than allowing them to turn out. Stay in Eka Hasta Bhujasana for 20 to 30 seconds, and then, as you exhale, gently lower your buttocks and left leg to the floor.