G. F. Schleebenhorst said:
By any measure we've devised, dogs and cats rank about even in intelligence. Dogs are better at learning the kinds of things that fit the life of a social animal and cats are better at the those that fit the life of a solitary animal. Individual dogs and cats differ more from one another in intelligence than the average dog differs from the average cat.
They you're not keeping him clean. Cats clean themselves, which is something a lot of people appreciate about them. Dogs need to be bathed.
And they eat their own shit.
Every mammal has to have a way to maintain the bacterial culture in its gut. With all Canis species, it's by eating all parts of their kill, including the intestines and their contents. They can't do that since we stopped them from hunting--or even from scavenging the leftovers from other predators' meals.
All they can do is eat stool. Preferably that of other animals, but their own if they're forced to. They're recycling the bacteria that survive in the stool for a while.
We exacerbate this by feeding them commercial food with preservatives that kill off the culture.
A dog who eats his own stool is
desperate and needs your help. First off, switch to a brand of food that doesn't have preservatives. Get him jump-started by giving him a spoonful of yogurt, more for a big dog. You may need to give him regular doses of yogurt, once a week or something like that, if you find him going back to his old habits.
And remember that dogs
are creatures of habit. If he's been doing this for a long time it won't be easy to stop. Keep the yard clean so there's nothing for him to find, and eventually he'll get out of the habit as long as he has no physiological need for it.