Again, we're back to "could haves". Suggesting the dog would obey for over 10 hours is a bit hard to accept. We have to think logically about what is the most likely behavior for a dog in a bloody crime scene. Of course it's that they will most likely get into the blood.
Is there any logical reason why the killer would lock the dog up in a room and then release them afterward --- so that they "could" get into the blood? Why not keep him where he's contained or put him in the fenced yard?
Also, why didn't MF put the dog in the fenced yard when she exited the house? Why didn't any of the responders see him? You can say that she was too distraught but would she really just let the family dog run loose? That is what we're to believe happened. And no one saw him until the neighbor finally noticed he was loose and took care of him.
There is no logical explanation about the dog.
iirc, Meredith could not remember in her testimony exactly where he was in the house when she arrived.
JMO