animal control. Ours told us we had to write a letter and send it in, then they would talk to the owners. Then if it kept happening we could call it in and they would come back and maybe take the dog and/or fine the people. But be carefull doing that cause it is not kept a secret who reported it, they will tell them, or (like ours does) they can charge them a small fee to get the whole report that says who turned them in and all. So if you know the owners and you think they might get mad at you and try to get back at you then I would try to think of another way....also if the dog is loose you can call animal control or an animal shelter and report it and they will come pick the dog up and they owners have to go "bail him out". That sometimes you can get away with not giving any personal info out..hope this helps