You can always send an anonymous letter to the owner of the dog through
Dogs Deserve Better Home: No Chained Dogs! I did this before and had letters sent to the owners of the dogs. It helped somewhat. They ended up getting rid of one of the dogs. I couldnt save both but at least it helped one more dog
Email DDB and ask them to send a letter or sometimes even better they sometimes get an area rep to go out to the house and talk to them
info@dogsdeservebetter.org