My Gizmo is a climber also. I usually have a chair sitting beside the x-pen that I have her pups in and I forgot to put it back yesterday after I finished cleaning the pen. She usually comes and gets me to put it back but this time she just jumped up and hooked her feet on the top and jumped over it.
I couldn't believe it. It is amazing how high they can jump. I have another gate that is 48" tall and she gets over that too. She is quite the escape artist.