DEAR DR. ROACH: My son is studying aviation maintenance, and the instructors tell the students to expect random urine tests for drugs when they are employed. Drinking alcohol is fine, but using marijuana and other drugs are cause for losing your license and thus your career. Recently we were walking around Boston for a day and we smelled pot frequently. Recreational and medical marijuana are legal in Massachusetts. He asked if one could fail a urine test by inhaling secondhand pot smoke.