This is very annoying, I have a similar problem and use a dog whistle that can operate at different frequencies, low frequencies for older dogs and high frequencies for younger dogs. They have a range of two miles they can be carried around on a lanyard and used when persitent barking occurs I dont use it when guests arrive next door. Timing is every thing and after a week of training the neighbours dogs things should get quieter and wonder what is this strange noise. It is a good idea to use the whistle out of site of the dog owners as some owners like their dogs to bark as a detterent to unwanted guest. But persitent barking for no reason is a menace.[I]