My guess would have been a grudge against the owner, actually, not the dog. A grudge against the dog would almost have to be a neighbor, not someone who'd have to drive there. But someone who wanted to hurt Rhonda for reasons totally unrelated to Toby (ex? disgruntled colleague?) might come over and try to harm Toby just to hurt her.

(An evil person, of course. I am NOT suggesting that would be a reasonable course of action!)

Is Toby being kept inside overnight for the time being?