Shama barks more than we'd imagined she would. She goes out on the deck and barks and neighbor dogs barking in the distance. Yesterday, we took her for a walk at Lowe's (pet friendly), and she barked at customers walking in the distance. Last night, we watched an episode of Game of Thrones, and she barked at the horses. This morning, she barked at the dog featured on the CBS show, "Lucky Dog." At agility training, she'll bark at the other dogs running the course unless I cover her crate with a towel so she can't see. Barking is a topic I keep meaning to work on with Shama. Here is a link to six different videos presented by Kikopup. Maybe one or more of them could help you?
When Shama was little, I wanted strangers to be able to give her a treat in order to teach her to like everyone. Later, a obedience/agility friend/trainer suggested that my DH and I should be the ONLY people who give her treats so that she always stays very connected to us. She suggested we put her in a sit and give her treats as she allows children/strangers to pet her. You might try that. That way, Lio could feel safe because you and near and giving him treats even as he's allowing a "stranger" to touch him. Maybe then he'd think, "Should I be scared/stressed? Nope. Mom's here and giving me a treat." (I do still like to allow little children to give treats to Shama since it's such a thrill for them!)
Here is a photo of Shama watching "Lucky Dog." She barks for a while then settles in to watch intently . . .
My friend's Havanese had the same bark bark attitude. He was harmless but he seemed to always want to sound off at any excuse. I read an article about dogs needing a pack leader. If you as an owner relinquish that duty, then your dog will feel the need to take that spot of "protector" by always having to stay alert. It is wearing on a dog to have to feel responsible for alerting whenever necessary. The dog eventually never feels at peace.
I mentioned this in a prior post, that when I saw Tux beginning to exhibit those behaviors (alerting at a sudden noise, or barking at the door because of noises outside our condo.) I knew I had to find a way to nip it in the bud. When he would bark at the door, I would distract him with whatever it took to rewire his brain. I could say calmly and in a high soft happy voice, "Hey Tux, it's okay. There's nothing out there. Come see me. Come see mom". (I NEVER got up and moved toward the door). The tone of voice is crucial. Tux realized I wasn't concerned, and he was distracted because I wanted him to come to me. When he did, I would praise him, talk to him, distract him, play with him, whatever it took to change his focus from fear guarding, to "Oh, its play time with mom!!!!"
It takes consistency and patience to keep your emotions in check so that the dog doesn't sense your hypersensitivity and translate that into, "Oh yeah, now we both need to bark at the door, Mom and me together!!" If they learn that whatever they were barking at is something you could care less about, but instead you pay attention to them CALMLY, eventually they will learn that a sudden knock or noise or animal walking nearby doesn't concern you and so they let it go.
Visitors knocking on the door requires a bit of practice. If you have to get to the door, don't run, or act excited in anyway especially if your dog is coming unglued. Don't let them get in front of you. Position yourself in front of the dog and let body language show you are the leader and YOU open the door. Tell guests to ignore your dog (not to even look at them) until everything is calm. It really really works but takes time.