I mean read this from that site:
U.S. Customs Inspectors Seize 10,000 Steroid Doses
Smuggled on Ferry from Santo Domingo
On May 23, 2001, at the Port of Mayaguez, Jose Luis Maldonado Ortiz and Maria Albania Acosta Mejia were arrested for attempting to smuggle in the gas tank of their vehicle 10,000 anabolic steriod pills and injectables into Puerto Rico, with an estimated retail value of $150,000. Both had arrived from Santo Domingo, Dominican Republic, aboard the ferry "Millennium Express."
A U.S. Customs canine alerted positive to drugs in the gas tank area of the vehicle. Removal of the gas tank revealed secret compartments filled with thousands of anabolic steroid pills and injectables.
I mean it was in the gas tank for christ's sake, and they found it. And as far as not being tipped off, how the hell are you supposed to know that until it's already to late and you're busted.