A Las Vegas shooting from a high-rise hotel that killed 59 people in a packed concert below has forced other cities to examine their tactics for dealing with this kind of nightmare scenario.

In New York, which hosts Times Square New Year's Eve and other events surrounded by high-rises, police say they use rooftop snipers to scan for threats, and make security sweeps of nearby hotels.

But they acknowledge there's only so much that can be done.

Chicago's mayor says his police have conducted a dozen training sessions ahead of this weekend's marathon.

Austin, Texas, police say they will have an increased presence for a music festival expected to bring 75,000 people a day to the downtown, but organizers say they will offer refunds to those uncomfortable with attending.