So many less deadly but easy & cheap ways of terrorism

I understand we're doing the best we can to protect our home but if you think about it, there is only so much we can do.


I mean, what is to stop an Al-Qaeda member from flying a remote controlled plane with some sort of explosive into a crowded street? Or whats to stop an al-qaeda person from wearing a waist pack with a grenade inside and strolling into a mall or ambushing a van full of people at rush hour? Sure, these attacks would kill 10s or 20s rather than the big numbers, but the smaller attacks are scarier than the big ones because it makes you realize it can happen anywhere, anytime.

What are we doing to stop these smaller scale yet equally terrifying things?