Wow...I like it! But does that mean that you presume Stallord was evil in his living state? In that case, my Lanayru theory does not support yours. However, for the sake of the thread, your theory actually supports the possibility of him being Volvagia or some other beast.
Maybe evil, maybe just feral, I doubt it was once good, why would it have been killed in the grounds if it was a good being? But definitely not Volvagia, otherwise he could fly or even dig out. I was thinking along the lines of a previously unseen beast, possibly extinct now, nothing of great intelligence or otherwise notability.
In any case if you elaborate on your theory fully it may gain more support.
Memories of the world
before the fall remain...
But the light of dawn doth never change,
nor e'er the hearts of men...