While we have no way to know for certain, do you think Arianna could have been the one to get the dog for him? (just speculating.)
My mental backstory for the "big guy" is that he is a mutt that Luthor couldn't get rid of and it's tenacity was intriguing to him.
CLARK: No. I'm just worried I'm a jinx.
JONATHAN: A jinx?
CLARK: Yeah. Let's face it, ever since she's known me, Lois's been kidnapped, frozen, pushed off buildings, almost stabbed, poisoned, buried alive and who knows what else, and it's all because of me.
-"Contact" (You're not her jinx, you're her blessing.)
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