G.,
I agree with the previous poster who recommended going to your neighbor and politely explaining the situation, giving them a chance to address the problem first. It's the right thing to do (unless there is some other information we don't have and that makes you fearful to approach them). They truly may not realize what is happening with their dog when they are gone.
If you don't get any relief by talking with the neighbor, know that every city has laws regarding animal control, and that includes barking. Go online, and look up your city. It may take some navigating around your city's website, but you'll find the information you need and a contact number.
I would not throw anything over the fence for any reason. If something happens to the dog (it chokes, has a reaction, gets sick, etc.), you could be held responsible. Don't take this into your own hands. Instead, if you can't resolve it with your neighbor, call a neutral party (animal control).
And since you asked, as a former dog owner, I will tell you that I don't think it is okay for dogs to bark ALL DAY long. Some barking in small doses is understandable, but constant barking is unacceptable, and that is why there are laws that require owners to take action to correct it.
When you live next to a farm, you know what you're dealing with (responding to another poster below). In suburban neighborhoods, you don't expect to hear constant animal noise. What many people forget is that there are so many individuals (medical personnel, law enforcement, firefighters, taxi drivers, airline personnel, etc.) who work on 3rd shift and must sleep during the day in order to be well-rested and alert enough to perform their duties safely.
Can you imagine, for example, being an ER nurse whose been kept awake all day because of a barking dog, and then being expected to dispense medications, provide treatments, attend to patient needs, and document charts accurately while being sleep deprived?
Just a thought for those who don't think it's a big deal.
I wish you the best in resolving this issue quickly and peacefully.
J. F.