Dog question: Why does he do this?

[MacMagus]

Dogs don't ordinarily pee where they eat. They've got instincts against that.

My first guess is that he's got a food allergy since this seems to be linked to a change in diet. Can you put him back on his old food for awhile to see if he gets better?

If the problem persists or if you see other symptoms, he may have a serious medical condition. Take him to the vet.