That's true, they can't watch every mobile muslim given their limited resources. They are glad for whatever luck brings them, as with the foiled attack on banks.
http://www.bbc.com/news/world-europe-41185913
"...We know they go to buy a camera, we know particularly they leave the hotel in the evening and they go off to spend a long time in front of the Eiffel Tower. Then they go back there the next day before setting off for Spain," he said, citing a study of the men's mobile phone geo-location...
The US has been aggressive lately and together with the Russians and local allies, the partners have scored intel breakthroughs that should provide some respite.
http://www.latimes.com/world/la-fg-i...908-story.html
...In the most dramatic gain, U.S. officials over the last two months have added thousands of names of known or suspected Islamic State operatives to an international watch list used at airports and other border crossings...
Problem is, Islamists now rely on just terror operations, which tend to escape notice by the services.