"My dog needs a best friend. That is why I take him to the dog park."
Your dog's best friend should be YOU; it should not be your neighbor's dog, the dog he grew up with, or the dog he met at the dog park.
Dogs crave for an intimate relationship with you. They want to have you lead them, inspire them, direct them, and protect them. They crave for a relationship whereas they can lean on you, follow you, and be one with you.
Please honor that.
"Who is your dog's best friend?"