How to plan for the unexpected. That's the greatest challenge facing security force leaders ahead of the London Olympics.
With just one month to go until the sporting world focuses its attention on the British capital, organisers have accounted for every known threat.
So what is the greatest fear?
"The unknown," said National Olympic Security Coordinator, Assistant Commissioner Chris Allison, visibly tired by his unrelenting position within the Olympics hierarchy.
"There are just some things that we cannot predict and cannot plan for. As an example, who could have forecast the Icelandic volcano which brought air traffic to a standstill in this country?"
Four broad areas of security which have been considered by Games organisers, are described by Mr Allison as: terrorism, protest, natural hazards, and serious and organised crime.
"We've looked at all terrorist attack methodologies and we've made sure that we've put in place appropriate control measures to deal with all of those attack methodologies," he said.
"Whatever they have used before, whether it has been devices, whether it has been Mumbai-style ... those are the sort of things we've considered and we've put in place appropriate security regimes."
Entry to Games venues will be as stringent as passing through international airport security, including bans on liquid of 100ml or more. Sunscreen is no exception.
Despite reports of a large-scale protest in London on July 28, authorities say they have not been officially notified of any such plans and maintain demonstrators "do not have the right to stop the Games".
On the organised crime front, Mr Allison said some 175 people have been arrested in the UK on suspicion of profiting illegally from the Games through activities such as ticket touting.
"We are confident in our preparations, we believe that we can and will deliver a safe and secure and spectacular Games, but we remain vigilant, we will leave nothing to chance," UK Government security spokesman James Brokenshire said.
"We've sought to put ourselves under pressure in these scenarios testing our response to terrorism and other security threats - accidents, transport disruption, extreme weather - it's all of that broad range of issues that we've sought to test and prepare for."
Part of that testing has been a military exercise analysing the viability of deploying missiles near the east-London Games site, including on residential buildings.
While the final green light is yet to be given for the proposed use of surface-to-air missiles around the Games hub, defence specialists say there would be no risk to nearby residents.
"The exercise achieved its objectives and I'm confident we are well placed to deliver this important role," Defence Secretary Philip Hammond told the British House of Commons.