My husband has had hard to flush smelly and oily stool what can be wrong?

Too much fat: Floating smelly stools are a sign of fat in the stool. This can result from poor digestion of fat in food, eg from a lack of an enzyme called lipase, which is made by the pancreas. There are several causes for this and you should see a gastrointestinal specialist if this continues . Can also try switching to a low fat diet for a couple of days to see what happens.