Hi
Cindy that is excellent noticing. One of many little tips is to lift the front toes off the ground which also has the effect of drawing the weight back towards the hips.
When people’s legs slip it is usually about weight distribution. This can be from foot to foot through the hips (notice if either or both set of toes are taking the weight), and/or from front to back (make sure you stretch up through the arm, while pushing the other elbow back into the knee and that the lower arm connects at the right spot on the leg – mostly people lower their arm too far).
Namaste
Gabrielle 🙂