I can empathize with you completely!! I met a couple with 2 Chihuahuas years ago, they were on the path to making the dogs barkers and biters. A shame.
First you need to know it is the owner who is going to be your biggest stumbling block here, I love the "owner story" which is the story the owner comes up with to rationalize their dogs bad behavior - it is always something (heavy sigh).
You can try and speak with the owner again letting them know that the problem has become a nuisance and is unacceptable. Let them know the barking is impacting your health and then offer to refer them to a local trainer or to someone who can help this can be done in a letter, by phone or in person. I can tell you right now the success rate in dealing with an owner like this is very small. Most owners will be polite to your face (or not) and go right on doing what they have been doing..
You next option is to contact the humane society or local police department. You will need to let them know this is not a one time issue - you must let them know it is an ongoing problem and it happens 24/7. The best thing you can do for yourself in a situation like this is to start documenting the problem. Keep a log of the times the dogs are barking, time and day and for how long and if it woke you up or interrupted your phone calls or bothered your dinner party. If you can video tape the dogs or just the fence where they are barking from if you can not see them from your side of the fence - the law will better be able to serve you if they know just what you are dealing with. A video - even if you can not see the dogs but can hear them is a very powerful statement, especially if you can say - here is 56 of the dogs barking in a one week time period. In the mean time, you can make the area near your property unwelcome to the Chihuahuas.

******The following is not fair play**********************

Many dogs dont like the smell of bleach - it is potent and they tend to stay away from it. You can spray Repel or some other dog repellent down and you can follow that up with putting out some opened pint sized bottles of bleach.
IF THAT DOES NOT WORK - You can go get some of that Alaska Liquid fish fertilizer - which will probably keep everyone in the neighborhood away from you and you will probably get some weird looks when you go to the store because you will smell like rotting fish if you accidently splash any on you. Pouring the Alaska Fish emolient near the fence is going to have the Chihuahuas trying to roll in the stuff. The owner will not be happy about their dogs smelling like rotting fish and viola the dogs are not let out again....This can be reapplied as necessary AND your plants will love you for it. The hard part will be in keeping your dogs from rolling in it ;)
Good luck, please repost and let me know what you decide and how it goes....

I can empathize with you completely!! I met a couple with 2 Chihuahuas years ago, they were on the path to making the dogs barkers and biters. A shame.
First you need to know it is the owner who is going to be your biggest stumbling block here, I love the "owner story" which is the story the owner comes up with to rationalize their dogs bad behavior - it is always something (heavy sigh).
You can try and speak with the owner again letting them know that the problem has become a nuisance and is unacceptable. Let them know the barking is impacting your health and then offer to refer them to a local trainer or to someone who can help this can be done in a letter, by phone or in person. I can tell you right now the success rate in dealing with an owner like this is very small. Most owners will be polite to your face (or not) and go right on doing what they have been doing..
You next option is to contact the humane society or local police department. You will need to let them know this is not a one time issue - you must let them know it is an ongoing problem and it happens 24/7. The best thing you can do for yourself in a situation like this is to start documenting the problem. Keep a log of the times the dogs are barking, time and day and for how long and if it woke you up or interrupted your phone calls or bothered your dinner party. If you can video tape the dogs or just the fence where they are barking from if you can not see them from your side of the fence - the law will better be able to serve you if they know just what you are dealing with. A video - even if you can not see the dogs but can hear them is a very powerful statement, especially if you can say - here is 56 of the dogs barking in a one week time period. In the mean time, you can make the area near your property unwelcome to the Chihuahuas.

******The following is not fair play**********************

Many dogs dont like the smell of bleach - it is potent and they tend to stay away from it. You can spray Repel or some other dog repellent down and you can follow that up with putting out some opened pint sized bottles of bleach.
IF THAT DOES NOT WORK - You can go get some of that Alaska Liquid fish fertilizer - which will probably keep everyone in the neighborhood away from you and you will probably get some weird looks when you go to the store because you will smell like rotting fish if you accidently splash any on you. Pouring the Alaska Fish emolient near the fence is going to have the Chihuahuas trying to roll in the stuff. The owner will not be happy about their dogs smelling like rotting fish and viola the dogs are not let out again....This can be reapplied as necessary AND your plants will love you for it. The hard part will be in keeping your dogs from rolling in it ;)
Good luck, please repost and let me know what you decide and how it goes....

I feel your pain. Where we lived previously, a couple moved in on the side where our bedroom was. Their Chihuahua yipped and barked CONSTANTLY from the time it hit the door to go outside. They were night-owls and allowed the dog out all hours of the night. Thankfully they moved in just a few months before our planned move or I think it could have gotten ugly. The neighbors on the other side also had 2 dogs that whined and barked from the minute they were let out. They completely ignored them for hours at a time, but at least it was in the daytime. I just don't see how they couldn't hear it when I could very plainly from inside my house with all the windows and doors shut and the air conditioner running. We now live in the middle of 5 wooded acres, if someone's dog barks here it's hardly noticeable.

Mazer, I love you. I never knew you had a devilish streak.

But along those lines: vinegar?

go for it. ps sorry for the double posting, my computer went crazy

The whole idea is to annoy the most sensitive parts of the dog without doing harm, if you open a bottle of vinegar, you are not going to get much reaction unless you stick your nose close to it. But Im remarking on that as a human being, dogs may not like the smell. I know for a fact they dont like the bleach and will start sneezing, alcohol will do the same but the alcohol will dissipate quickly. Bleach has staying power, as does garlis (especially when the oils are released by roasting but I know my friends mother innocently ruined her entire neighborhoods Thanksgiving dinner by applying the Alaskan Fish fertilizer, which was only applied once and the smell lasted an entire day.....That is why it is your best bet. It not only will have the dogs very curious about the smell, which may shut them up, but it WILL assault the nose of the owner, a double hit. Placing some on the ground basically under the fence and then leaving the bottle out would probably be your best bet. I will be curious to see what happens. Please report.