Not all dog owners like neighbors getting into their faces and telling them how to manage their dogs. Some can get very irate. The best thing you can do is get a good description of the dog and address where it lives and even pictures of the roaming dog if you can. Next, alert animal control. They can try and catch the dog and educate the owners. Not only is being caught safer for the dog, but it is safer for the community. If the owners do not care, maybe they do not deserve to have the dog in the first place. Animal Control can help the dog find a better home if the dog can be put up for adoption. Animal Control Officers are all about public and pet safety.
Leash laws and other laws designed to prevent roaming dog laws are here for a reason. As responsible dog owners, it is our duty to follow them. Even if your community has no laws, we still need to think about safety. If not, we are not only putting our dogs but also our community at risk.