This is our rescue dog Charlie, he is 7 years old and has a laid…

This is our rescue dog Charlie, he is 7 years old and has a laid back personality, even when he was a puppy. I was wondering if anyone knew what breed he is? We’ve never done any testing.
He did used to nip at our heels when we played in the backyard, which makes us think a collie or other herding dog breed. And his coat is soft and silky, never trimmed.
I would love to see what you think!