If you have any reason to believe it is a Guard Dog , then there are laws regarding the behaviour pf the dog and its control.
Also the clear signalling to make the public aware.
The Guard Dogs Act 1975 prohibits the use of a guard dog on any premises unless there is a ‘handler’ capable of controlling the dog present on the premises and the dog is under the control of the handler at all times. The only exception is where the dog is secured so that it cannot go freely about the premises; or where another handler has control over the dog
The Act prohibits a person from using or permitting the use of a guard dog at any premises unless a notice containing a warning that a guard dog is present is clearly exhibited at each entrance.
Many years ago my DD was terrified of dogs , and funnily enough, it never occured to me to "teach my child to not fear dogs" , I thought it SO much better to let her decide for herself if a dog coming round the corner was more of a danger than running onto a main road .
Face Pams.
It curtailled many places we could go.
Roll on a few years (she isn't afraid now) two barky dogs next door .
Sometimes I do shout at the dogs to STFU (in my defence , the owners shout Shut up Bobby so I figure its the language they understand .
But I have knocked on the door at stupid o'clock when the barking has gone on 2 hours.
Or when they've come into my garden.
You need to put the needs of your DS above this dog.
You cannot prove they let it out to scare your DS but you can tell them the noise is untolerable.
You can download some details about noise pollution.
But if he is a Guard Dog , think about it in the same way as an alarm. They are welcome to have an alarm. They are not welcome to let it ring for hours on end .
And feeding a strange dog? No.
Chocolate? You'd get the Vets Bill if it was my dog.