what must countries do to stop these terror attacks?

[Bordo-Bereli]

Nearly all countries have lived the terror events.But nobody can stop them,they can bomb in a city for example,how do they enter the city with bombs?Doesen't any police or soldeir or agent know that such an event will be?What must they do to stop these attacks?
Terrorists can enter to USA and destroy twin towers,El-Kaide's militans bomb in Londra,İstanbul and the other cities.Can't the cities take different measures?
And ,I want to ask something,which country can struggle to terrorism best?

 

[EnigmaNZ]

Very hard to stop them in the west due to the freedoms in these countries. After 9/11 there was a plan in the US to target all young arabs with additional checks before allowing them to embark on aircraft, but it was stopped by the head of transportation. Being japanese and remembering the internment camps of WW2 in the US he decided it would be racist to target any one racial group as terrorist. In non western countries it would be easier as civil rights are largely non existant. With freedoms come dangerous times.