Dogs will chew on rocks and concrete for unknown reasons. This may be when they are puppies, but it can be when they are older as well.
It could be a variety of reasons, including feeling good for some reason: taste, feeling, boredom, compulsion, diet/nutrition, medical issue, simply a dumb puppy thing to do, etc.
My friend from elementary school had a dog that would chew on rocks as a puppy.
He eventually seemed to grow out of it, however I have learned that you should try your best to make him understand "No" or "Leave it", and then reward the puppy when he does leave it, however, you must do it in a way where he does not think he is being rewarded by chewing rocks.
Some dogs are more prone than others. Here are things to keep an eye on to learn why.
- Age and breed?
- What are you feeding?
- Does he still readily eat any time he's fed?
- Does he ever turn away food?
- Specifically what kind of concrete/rocks?
- Large stones?
- Same place?
- Random places?
- Place in your yard?