Awful dog farts. . . . .?

My dad's dog just moved in with me. He poops about a million times a day, likes to go on walks for MILES. And the worst part is when he finally lays down for the night he starts farting. And they are awful, clear the room, something-must-have-died-up-there farts. Can I get him to stop? Feed him something different? What can I do!?