Tens of thousands of people will gather this weekend for the Austin City Limits Festival, a two-week music festival about a mile from downtown Austin."It's gonna be the safest part of the city to be in during both weekends, just because of the sheer number of officers that will be present," said Brian Manley, the chief of the Austin Police Department, during a press conference this week. Manley said the department will have officers inside and outside the festival, with heightened attention to threats from outside the gates."We want folks to come out, we want you to enjoy yourself," he said. But he also warned that "we live in a world now where you cannot protect against every single threat."That was made all too clear to police in Austin and across the country on Sunday night, when the deadliest mass shooting in recent U.S. history left 58 people dead and close to 500 injured at a country music festival in Las Vegas. It was the just latest assault on a music venue, after the mass shooting at the Bataclan theater in Paris in 2015, and the suicide bombing outside an Ariana Grande concert in Manchester earlier this year.The Las Vegas shooting is a chilling reminder that big public concerts remain a soft target. And the industry is still grappling with what lessons it should draw from the massacre."A nightmare scenario" is the way Chris Robinette described Sunday's attack. Robinette is the president of Prevent Advisors, the security branch of Oak View Group, a company that advises major sports and entertainment venues. The shooter fired from the 32nd floor of the Mandalay Bay hotel, which is separated from the concert site by a major interstate highway. Robinette predicted that the gunman's distance from the event would force outdoor venues to pay more attention to potential threats from outside the gates."If we're talking about outdoor events, it's important that we think about adjacent buildings," Robinette said, including "rooftops and balconies and things where threats might now originate, that they didn't historically come from. So that's becoming a very, very relevant issue at this point."But the attack also underscores that there's only so much the concert industry can do to protect large gatherings."It's impossible to secure them to the point when you can prevent any kind of violent attack, and still be accessible to the public," says John Cohen, a former counterterrorism coordinator at the U.S. Department of Homeland Security who's now a professor at the Rutgers School of Criminal Justice in Newark. He argues that it makes more sense to try to prevent attacks through better police work, and more cooperation with the public."You could build higher fences, screen people more extensively as they come in. You could've put more police inside and around the venue," Cohen said. "And none of that would have stopped this attack."At least one security expert thinks there's another lesson the concert industry should take from the Las Vegas shooting."The situation was made worse by the failure to attempt to evacuate people, and possibly save a life or two, or prevent injuries," said Paul Wertheimer, co-founder of Crowd Management Strategies, a firm that advises concert venues.Wertheimer has studied YouTube videos that members of the audience recorded in the moments during and after the shooting at the Route 91 Harvest Festival, and he was alarmed by what he saw.When the gunfire begins, headliner Jason Aldean stops singing and runs offstage. The lights go dark."And nothing happens, as far as the crowd. No direction. No lighting. no pre-recorded message. Nothing to help the crowd find safe haven or shelter," said Wertheimer. "Nothing was said, and 23,000 people were literally left in the dark as they were being shot at that. That's what alarmed me."In the chaotic moments that followed, Wertheimer says, it's easy to see how people could have gotten hurt. Las Vegas Sheriff Joe Lombardo confirmed that some of the injuries sustained on Sunday night were the result of trampling, or resulted from concertgoers trying to escape from the venue. But it's still unclear how many were hurt, or if any of their injuries were fatal.Las Vegas Village, the site of the Route 91 Harvest Festival, is owned by MGM Resorts International, the same company that owns the Mandalay Bay hotel. A spokesman did not respond to requests for comment.Wertheimer argues that the festival and venue should have provided lighted exits and could have used recorded audio or video messages to instruct the crowd on how to escape in a more orderly fashion, though he concedes there's no guarantee those measures would have saved lives."There are dangers in every step in a horrific situation like that," Wertheimer said. "But doing nothing is probably about the worst you can do." Copyright 2017 NPR. To see more, visit http://www.npr.org/.