What about dogs?
 

Lest the idea stay tucked away in a thread about something else...

Seems like the best next thing. The only drawback I've seen - at the ferry between Portland, ME, and Yarmouth, NS - is once one dog hits on one thing, she stops and sits or gets excited about it, while another thing gets by. But the solution, lots of dogs, works for me. :) (These dogs aren't attack or protection dogs. Those are wholely separate breeds and training plans. Think Beagle or Golden. To these, an explosive is almost as good as a ball.)

Sounds exactly like what happens at checkpoints now. :D

Dogs can be good, but they can't work for long periods of time without breaks. The training time is long, which means deployment can't be made quickly. Training of the handlers is also a concern. A five-week course just doesn't cut it many times. In addition, with the additional pressure being placed on training more dogs, there appears to be more "puppy mill" attitude out there.

You can easily substitute 'people' everywhere you have 'dogs' in that paragraph.