My pair go ballistic (esp. the female) when other dogs are walked down the sidewalk in front of our house. This applies if they're in the house or out in the back yard and see the other dog through the side railing fence. But if I have them on leash out in front, in the yard, they don't react at all if someone walks a dog past us. Why is it okay for another dog to walk down "our" sidewalk when they're out there, but not when they're in the house or back yard?
Who knows. Dogs are weird.