Terrorists are not a credible threat.
FIFY, at least in America.
41,000 Americans die each year in vehicle-related accidents (source: ntsb.gov)
785,000 Americans die each year due to heart disease (source: ahajournals.org)
580,000 Americans die each year due to cancer (source: cancer.org)
0 (as in Zero) Americans die each year due to Terrorism - it isn't a recurring event. This year, 3 people died in Boston, due to "Terrorism". In 2001, 3-5,000 people died; in 1996, 1 person died.
Even if we had a 9/11 every month, it wouldn't even come close to Cancer or Heart Disease as a threat.
...so you can toss your duct tape and plastic sheets. Or use them when you paint your garage.