There is a major tendency for people to presume that further security measures will somehow save us from potential terrorist attacks. This presumption, however, is an outright fallacy. Nothing will completely save us from the eventual terrorist who wishes to exact violence on our soil. Nothing.
Look at Iraq. You have a nation that is completely occupied with over 140,000 troops. You have a country where there is no Bill of Rights. You have a country that is basically under military rule 24 hours a day. Yet still, violence is rampant. In fact, the U.S. death toll in Iraq has surpassed the number of American soldiers killed during the first three years of the Vietnam War. And this doesn't even account for the thousands of Iraqi civilians who have been killed as "collateral damage."
The inescapable truth is that we are vulnerable to any group that has the will to attack us. Our borders are vast. Our nation's enemies are growing, in spite of the four years of "War on Terrorism." In truth, it's a war that cannot ever end. After all, the day we claim victory in the war on terror is the day we leave ourselves vulnerable to attack. Thus, our leaders have chosen to commit us to what is, in essence, a war that cannot end-- a war that cannot truly ever be won.
So what can be done?
As Noam Chomsky says, "There is one simple way for the United States to decrease very significantly the amount of terror in the world, and that is to just stop supporting and participating in it." You see, the prevailing belief is that if somebody carries out terror against us or against our allies, it's considered "terror." However, if we carry out terror (or our allies do), maybe even much worse terror, against someone else, it's not considered terror, it's "counter-terror" or it's a "just war." Not only is this just a political game of semantics, but it's a losing game altogether.