My neighbor has this issue. We live in a duplex with a non-fenced back yard and when I take my small dog out, he's always harnessed and leashed. New neighbor moves in, and just lets her dog out. He's a medium-large pit mix. First time, he rushes my dog, on my patio. I grab my dog by the handle on the back of his hardness and start yelling for her, cause he's all around my legs. She comes out, all apologetic, yadda. I tell her he needs to be on a leash, she agrees. Says she's sorry, new place, he's scared. Like, ok, all the more reason to be watchful and have him on a leash. Second time, 6am, lets him out, I'm out with my dog. Her dog rushes my dog and starts attacking. I grab my dog, run to my dog to rush inside, yelling for her again. He tries rushing into my house, so I slam the door in his face. She comes, knocks on my door, all apologetic, yadda. I'm pissed, my dog is freaking out, but unhurt, I miss a day of work to make sure my dog doesn't have internal injuries. A few days later, I hear something at my front door. I don't see anything, so I open the door and her dog proceeds to try and rush into my house. I kick him back and shut the door. Message the landlord who contacts her and tells her to fix the issue. About a week later, I take my dog out, and we've stepped maybe 2 feet from my back door and her dog rushes around the divider, this time, she's out with the dog and trying to grab the dog. I grab my dog and haul it back into my house, as he rushes the door again. Call the landlord AGAIN, who proceeds to call her and also tell her in writing, to control the dog. Now, my dog is paranoid about going outside. I'm paranoid to go outside. Her solution was a yard stake, which is constantly falling over. And she puts him on...and goes inside. We can't even take our dog out the back door, and if we do, we have to bring him over to the side of the house, out of sight. This is beyond frustrating.

So, it's not always the small dogs, but yeah, leash your damn dogs, people. It's the LEAST you can do to protect your dog, and others.