but I would really appreciate if we could stay on my original questions
I thought the question was how you can keep your dog from nuisance barking in your yard, which probably annoys you just as much as it annoys your neighbors.
You have to understand that this nuisance barking is a problem that you have created by turning your dog out and leaving him outside unsupervised, whether you're in the house when this occurs or whether you are gone from the premises altogether. Your dog barks because you leave him out in the yard and he does not enjoy being stuck out there alone with nothing to do. That is simple fact.
A no-bark collar will prevent him from barking, but it does not fix the problem. The problem is that your dog is bored and lonely. Once you take the bark, he won't annoy you and your neighbors when you turn him out to amuse himself. He will, however, find other things to do to amuse himself and they will probably be just as annoying - like digging up the yard, tunneling under the fence and running loose, etc.
If you want to fix the issue, be outside with your dog and provide him with proper exercise. When you have a dog, especially a large, energetic breed such as a German Shepherd, you may need to sacrifice sleeping in for the sake of properly providing for your dog.
You may feel that dogs should never be outside by themselves but that doesn't mean that everyone feels that way. If my dogs were never outside by themselves, they wouldn't get near the playtime and exercise time they do now. My dogs are never outside when no one's home but they are outside when no one is out with them.
And AgileGSDs case is very different from the OPs - she has SEVERAL dogs who play with each other. The OP has only ONE dog who is left out by HIMSELF and bored.