Washington, DC, is famous for monuments that honor presidents or heroism during war. But in a recent contest sponsored by the Washington Post, the most popular monument is not on the National Mall in front of the Capital, but downtown in front of a fire station. And it is neither a giant in height nor reputation. Instead, the life-size monument depicts a Labrador retriever, gazing up at a fireman in a rumpled uniform, who smiles back at his faithful canine partner. Shelley Schlender reports.