I think I know what you mean about the knees. Sort of like they hyperextend sometimes. I'll work on that..
The tail is infront of the tree now but during the final composite, I will create a mask for the tree so the tail will be behind it.
Personally, I'm not too thrilled with the way the feet bend while the model walks but I'm still learning how to design more complex rigs. The rig I originally came up with for the feet allowed the toes to bend in any position I wanted however, this was achieved thru MEL scripts that I wrote and I could not find a way to make certain functions keyable so that they would play back properly. Oh well. There's always the next time...