National Park Service groundskeepers will be rolling out miles of fencing around the National Mall over the next few days as they prepare for the annual Fourth of July bash.

The barriers will have dozens of security checkpoints where people can enter the 146-acre Mall, a prime location for viewing Washington's fireworks display. Sections of the fencing can be removed quickly if there is an emergency.

Officers equipped with handheld magnetometers will examine purses and backpacks, and dogs will be there to sniff out explosives and drugs.

More than 500,000 people are expected to attend. "We're going to ask them to come early, be patient, limit the number of items that they bring," Sgt. Scott Fear, spokesman for the U.S. Park Police, said Wednesday.

"We believe that the National Mall will be a very safe place to be on the Fourth of July," said Fear. Street closures have not yet been announced, but parking will probably be extremely limited, Fear said, so people are encouraged to use mass transit to get into the city. The Smithsonian subway station — in the heart of the Mall — will be closed.