How socialized is the dog?
For example, my dog is poorly socialized with other dogs. He no longer barks at any humans (unless he's scared for other reasons) but any dog, cow, cat or anything he sees from the window he'll bark at them.
I have been training him, by correcting him each time he nuisance barks (I go to where he is, say "no bark" sternly, and a swat with a rolled paper if he keeps at it) but it hasn't eliminated the barking.
I think I will need to socialize him with other dogs (especially the neighbor dogs he most barks at) but haven't had a good chance to do so (no dog parks etc). What I'd do is walk them both side by side at a distance out of reach until they he's tired of barking and just ignores the dog. Hellifino if that would work.
And the last resort I'd try is a collar. From my research into it it doesn't sound like it's cruel (in some ways its less cruel than forever stressing your dog with discipline he's not fully understanding), but I'm not sure if it would be effective without the collar. In other words, the dog may just learn not to bark with that collar on, and that's not what I want. I don't want it to be a permanent thing.