Wrist strength

I'm starting to work on my planche. So far I am doing ok, even though my progress is slow (not sure if this is normal). I never thought that this exercise would be so hard on my wrists. In the book coach says he conditions his gymnast's wrist with liquid steel™ exercises, but we all know that book will take a while to come out. Can anyone help me with some exercises. Thank you.

Theres a good exercise in the wrist endurance sticky in the joint and flexibility forum. I also like using a rice bucket.