Meet Wylie, Rick's dog, who I take care of anytime Rick is indisposed. He's truly the best dog I've ever been around: well behaved, well trained, and otherwise a sweet, caring animal. He's the "puppy" in my life.
While he's visited with The Kids on more than one occasion, sadly it was Wylie who lost that battle — Loki stalked and hunted him, did wage battle with him, and otherwise left Wylie with a bloody nose and bruised ego to prove it. It was probably an entirely unpleasant experience for the alien intruder.
Grendel, on the other hand, didn't care. He ignored Wylie and made clear that he would lie about the house regardless of the canine's presence; if Wylie somehow interfered with that simple activity, only then would it get ugly. That only happened once; afterward Wylie left him alone — perhaps because Grendel was too boring compared to Loki.
Kako and Kazon want nothing to do with any dog, especially one so much larger than they as Wylie. They will generally find a place to hide (under the covers on the bed, for instance) if he happens to pay a call.
Loki's response, however, hasn't stopped me from bringing Wylie home, but it has certainly given me pause to consider his welfare in light of Loki's relentless attacks. In this case, if he's at my home, it's Wylie who needs protection despite the fact that he loves cats. Loki doesn't care and will hunt the trespasser so long as he's here.
By the way, Wylie loves to play Frisbee (along with a plethora of other games, like tug of war, fetch, catch, blankie [this game takes on many different personas due to the versatility of his blanket], and a myriad of other games). But he needs to play Frisbee, and he's quite exceptional at it. No matter how many times per day you engage in this activity, he never gets enough until he's had enough — then it's time to go in for a treat. Smart dog.