Stop armature legs from floating once open the file

I thought I’d try these legs, I edited from a spider file that was setup for the blender game engine. I basically have the box which holds it all together, and then another box which holds it all together.

So the armature for the leg is its own setup. And the character object is child of the armature of that object.

So the legs aren’t obvioulsy joined to the other part. It is parented and works okay in one file, but once save and close, and then open the leg structure is left floating.