I can only improve my own 'domestic security'.   Whether I do or have done so or will do so is hardly a topic I care to explore here.  

With the large number of 'soft targets' and the unpredictability of any specific threat,  we are all just playing the odds.  Unless you are surrounded by alert armed bodyguards 24/7, there is no true protection.  

I intend to live my life under the assumption that being involved in a terrorist attack is no more personally likely than being struck by a meteor.   If it happens, I'll go into my OODA Loop and go from there.