At least we know what some of that $51 billion in security is being spent on:

http://pandawhale.com/post/33808/the-sochi-2014-olympics-an-environmental-disaster-russia-outsideonlinecom

A crucial role in the protection of this hard-to-manage terrain falls to the "Spetsnaz" troops, the legendary special forces made up of officers from the Army, the intelligence services and the Interior Ministry. The elite fighters are comparable to the British SAS or the American Navy Seals, who were responsible for tracking down and assassinating Al-Qaida leader Osama Bin Laden in Pakistan.

The most famous Spetsnaz unit, Alexander Mikhailov's "Alpha" group, has already been deployed in Sochi for more than six months. The counter-terrorism specialists scour the city, Olympic Villages and sports facilities for explosives. They also make preparations for emergency operations and hostage rescues. "We've taken security measures here that have only been used before at G-8 summits, when we are charged with protecting Putin, Obama, Merkel and Co.," says one officer.

The Spetsnaz fighters' principle target are Islamist militants from the provinces in the Caucasus. Led by Chechen rebel leader Dokka Umarov, terrorists there want to win independence from Moscow. Umarov's goal is the establishment of an Islamic emirate of North Caucasus, governed by Sharia law. In July he called on his fellow Muslims to hinder the Olympic Games in Sochi, "this devilish dance on the bones of our ancestors," through acts of terrorism.