Dogs and puppies are opportunists. Puppies naturally want to investigate the sights sounds and smells of the world. Not having hands, puppies instead use their mouths to pick interesting things up and play with them. Creating a puppy-proof area of your house is a must if you don't want your dog to pick up bad habits like stealing things and chewing things you don't want them to. Managing the environment so your puppy doesn't have the opportunity to create bad habits is 1/2 of the solution. House lines, baby gates and playpens are all incredibly useful when you have a teething puppy! The other 1/2 is teaching your puppy an alternative, incompatible behaviour that gets them the same outcome.
Don't just say "No". Saying "No" might interrupt our pups from doing an inappropriate behaviour, but that alone doesn't give them enough information and leaves the dog to decide what to do next. With no further instructions, "No" itself will become irrelevant to the dog which leads to us humans escalating our behaviour out of frustration!
Instead of saying "No", tell your puppy what you actually want them to do and then reinforce that behaviour with something that they like. Instead of "No" say "Come", "In your bed", "Sit", "Down" etc. These are cues that actually mean something to your dog and gives them something else to do. When they are doing these things they can't be practising the inappropriate behaviour at the same time; problem solved!
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