Would caustic soda work? I'm thinking that if it's hidden in some doggy treat the thing would take at least one mouthful and that should be enough to seriously fuck up its throat and vocal chords. It probably won't kill it but that doesn't matter if it shuts up and there's the advantage that with the dog still alive the owner won't replace it with an even worse one.
Thoughts?
Well, my thought is that you're one screwed up individual to be thinking about feeding dogs caustic soda.
Trouble is, I'm screwed up too. I am woken by bow wow bloody wow every morning at 5 am and am driven nuts by it. Believe me I've fantasized about doing far worse things to that dog than giving it caustic soda. Problem is I asked my neighbour politely if she'd do something about it and the response I got was, basically, NO. The police weren't interested and my local authority are more interested in helping one-legged transgender muslim gypsies than those who pay their taxes. So I can't touch the dog as I've made several complaints and it would backfire on me.
So if you get away with melting the mutt's mouth, good on you!