Puppies routinely mouth everything in sight as a part of normal development, and even most adult dogs, natural scavengers that they are, enjoy grazing now and then. Eating things off the ground presents potential health risks. Stop your dog from eating things on the ground before he scarfs something inappropriate.
Keep a head halter and leash on your dog during walks. Head collars fit around the dog’s muzzle and make it more difficult for him to put his nose down and eat things off the ground.
Teach the dog to focus on you instead of things on the ground. Hold a treat in your fingers and call the dog’s name. Wave the treat in front of his face and pull the treat up to your eye level as you say “look at me.” As soon as the dog looks at you, give him the treat. When the dog reaches for something on the ground, give the “look at me” command to refocus his attention on you.
Encourage the dog to leave things on the ground where they belong. Sit the dog next to you and place a tasty treat on the floor. As the dog reaches for the treat, say “leave it” and walk him away from the treat. Reward him with a treat from your hand when he leaves the food on the floor and focuses on you. Repeat this command every time the dog approaches an item he could put in his mouth until the dog ignores things on the ground on sight. If the dog reaches for something on the ground during a walk, tell him to leave it and give him a treat.
Fit the dog with a soft muzzle if he continues to graze. A soft muzzle will keep him from extending his jaw, preventing the pup from picking up stuff and eliminating the risk of your dog ingesting something gross.