Is this dog on a leash? Is the owner walking the dog here? Either way I think it is perfectly within your dad's rights to approach the owner. I've also seen people on my block post up signs saying to keep dogs off of their yard. Irresponsible dog owners totally irk me so I feel your pain. This reminds of the guy walking down my block recently talking on his cell phone with his dog off leash. The dog ran into the street and I almost hit it. When I yelled at the guy (sorry, I have a temper
) he started cursing ME out. If that fails I say call your town every day until they do something.