When my son has to fart, he makes a point of getting himself close to the dog so he can shift the blame. He really digs into the story, too. It's not ever as simple as "Gross the dog farted!" He will get into a big long story about "man, that dog must have been eating some leftover tacos or something, because I think I smell pork !"
When I have to fart, I get close to my son and blame it on him.