One of the biggest armored-car companies in this sprawling Texas city has a message for would-be robbers: It is not worth the trouble, or your life. In response to a series of armored-truck robberies this year in the Houston region, the company, GardaWorld, has taken the unusual step of talking publicly and talking tough, even for Texas, about the lengths to which it will go to protect its cargo, its employees and the public. “We’re letting the bad guys know: We’re going to defend ourselves,” said Robert Hatchett, the senior manager for GardaWorld’s Texas operations. “They can expect, in one...