Eating Poop?

Unfortunately, my dog is a poop eater also. The thing is, he doesn't eat his own, he eats other animals poop. When we still had our cat, Tucker would get into the litter box and eat, so I had to get a tall box that the cat could get into, but Tucker couldn't. Now he also eats poo that other animals do in our yard. We don't have a fence (and can't really afford to get one right now) so I don't know how to keep the animals out of our yard. If I see the poo before he does, I keep him away from it. If anybody knows what to do about them eating other animals poo, please let me know.