7 montb old pup eats poo

I know he likes to eat his own poo so I'm very watchful when he goes potty to pick it up immediately. But today at the dog park when a dog went potty my dog ran over there and ate his poo. I swear I could have thrown up it's so disgusting. He's healthy and eats well so I don't know what his problem is has anybody experienced this before or have any tips because I'm at the point where I don't even want to touch him because I feel like he's just dirty.