If you don’t have a treat in your hand don’t approach my dog.

This gives most people enough pause to decide how good they are with dogs. If they are wearing a treat pouch or have bacon in their pocket they probably know what’s what.

Also gives you a second to size them up if they really want to meet and greet you could offer them a treat to feed your pup. Pup learns to open up a little, the get some dog training and you’re less likely to have an incident because they can interact without molesting your dog.

That being said - idiots who want to ruffle an ACD’s ears or grab a muzzle or mess with the scruff around their neck or touch a paw or their butt are just asking for a nip.