I couldn't find guava on any lists of toxic foods for dogs. I wouldn't worry too much about it since I couldn't find anything that hinted at them being toxic. I would imagine that in too high amounts that it would give him diarrhea though, so I would watch out for that. Other than that I think they are harmless for dogs.
Yeah, I couldn't find it on the list of toxic foods for dogs either. The good thing is that when he's alone in the backyard (I'm peeking at him through a nearby window), he only eats like one or two. No more than that... :smile: