barking dog

My neighbors have a barking dog, a dog that barks ALL day and ALL night. They leave it outside unattended all the time and don't seem to notice the 30 minute intervals of CONSTANT BARKING for no reason. I have dogs, 2 LARGE dogs at that, and they don't bark, but we also don't leave them outside unsupervised, ever. Now I understand why people have to keep dogs outside, but...ugh.

I've asked them to keep an eye on the barking (especially in the morning, and at night) because he's right by my bedroom window... but we've lived here for 3 months now, and the barking has gotten worse.

I've asked in person, and we've left them a note about it, I'm about to go out there and spray the dog with the hose and yell at the poor thing to shut up! Is there anything else I can do without being rude? Because frankly, I'm about to get rude. We've been very polite about it up until now, and I just cannot take it anymore!