The latest headlines have drawn attention to the vulnerability of packages shipped via commercial airlines and probing techniques, the reality is that probing techniques occur with startling frequency and a knowledge of them one of the best defenses against them. Sadly, many of the very people who need knowledge of trends in terrorist attacks, probing techniques, and methodologies and threats from various groups against their area, never receive it. Security guards, clerks, cargo handlers, and the worker level of many organizations are the best eyes and ears an industry can have to guard against these types of probes/attacks and yet they are usually the last to be trained on even basic awareness.
The most successful strategy in decreasing the threat of bombings lies in providing a broad awareness of what to look for and what to do when you find it. In order to appropriately face such extreme situations, you are best served by highly skilled, experienced instructors who not only know how real bombers think and act, but also have expert tactics on realistic capabilities and surprisingly easy methods to screen and search for IEDs that guarantee a safer, less vulnerable area in your organization.
This is simply the initial step to security. There is never a 100% solution to any problem, let alone a threat of bombings from multiple groups worldwide against the US; however, the current trend of leaving most people in the dark about what to look for and what to do when you find it is sadly leaving success up to luck for a majority of people.