my dd went through a phase when she would shake her crib too - enough to move it away from the wall, but I don't think she ever got the feet off the ground. She stopped after a bit (we did some wi/wo with that). You could bolt it - I suspect if you got a couple of good bolts, he wouldn't be able to move them - or at least it wouldn't be easy, so he might stop if he wasn't getting the movement he is getting now. I don't know if anyone else has any better suggestions for you......