Dog-barking deterrents

PLEASE tell me what works best for making dogs STOP BARKING! My two neighbors' dogs (2 great danes in one yard, 3 big mixed-breed dogs in the other) are making me want to pull my hair out.

I am retired and garden a lot - out in the yard more than not - they bark and bark and bark. I saw an ad for a deterrent that's some sort of gadget camaflouged as a bird house - suppose to work 50' away - anyone heard of this one - do you know if it really works?

Yes, I have spoken to them, written them letters and sent copies to the police dept., told them to shut up - as soon as the owners come home, they become quiet.

Please give me info. on what works for you. Thanks!