pronoun antecedents



Is there a rule about pronoun antecedents referring to the closest preceding name/noun? A friend says no, and cites Perdue Owl as her source. Near as I can tell, my friend is right; the Owl is silent on that subject.

Here's an example:

George dropped everything he was doing and took Bob to the hardware store where he bought a nail.

Friend would say that the sentence is clearly about George, so the pronoun obviously refers to him.

I say Bob is the closest preceding name, so the sentence is potentially confusing and it's time for a rewrite. But I can't cite a rule. Can you help?