some 80,000 people will turn out tonight for a concert by french dj david geguetta.ranteeing the safety of those crowds is proving to be a serious challenge for police. >> with one million foreign fans flooding into france for euro 2016, private security firms are on the front line. will deploy 900 guards in stadiums and fan zones across the country. we read them their duties as security guards. duties as their security guards. how to optimize every move. >> with the giant screens, wi-firants, its own network, and a concert hall, the paris fan zone resembles a small city. many fear so many people gathered in one place will make it a prime target. >> opening up an area like this for 90,000 people will act like a magnet for trouble and that's really worrying. should think fan zones simply be closed on match days but the government wants a memorable sporting event and says every precaution will be taken. yet a looming terrorist threat covered with a wave of protests means the force is spread exceptionally thin. as thingswe go ahead are in the knowledge we don't have the