As mayor, Lerner employed unorthodox solutions to Curitiba's geographic challenges. Like many cities, Curitiba is bordered by floodplain. Wealthier cities in the United States, such as New Orleans and Sacramento, have built expensive and expensive-to-maintain levee systems on floodplain. In contrast, Curitiba purchased the floodplain and made parks. The city now ranks among the world leaders in per-capita park area. Curitiba had the problem of its status as a third-world city, unable to afford the tractors and petroleum to mow these parks. The innovative response was "municipal sheep" who keep the parks' vegetation under control and whose wool funds children's programs.