It would be cost prohibitive to defend every airport that sends flights to the USA. We are not the police of the world and to act as such will only create problems for us and the countries we try to police. As such we can not save the world from terrorism nor can we force other countries to live up to our standards. Other more practical options would be to: 1) Set security standards for all incoming flights to be met by the airlines and their countries of origin and have TSA grade each flight with regards to the standard. Then flights not meeting those standards, from an airline or country of origin, should not to be permitted in the airspace of the USA. In emergency situations they can be routed to a military airports with the military on alert status. 2) Another option, which is xenophobic and should only be used in extreme situations, would be to quarantine all incoming flights away from domestic terminals having the passengers go through security screening and the plain searched for explosives and weapons. However, there is NO ABSOLUTE WAY TO DEFEND AGAINST AN ATTACK EITHER HERE IN THE USA OR ACROSS THE GLOBE. Defense is a reaction to attack and weapons were created to destroy and not defend.