Marijuana use before eQuip. Current Job Worries


So my situation is an interesting one. I work for a custodial job and was recently promoted to a new level pending background check. This job does not drug test although I would absolutely pass. They told me they want to place me in a Federal building so I need to obtain a non-sensitive, Low Risk (NACI) clearance for contract employees. I know the background portion I will be totally fine. No arrests, no tax problems. The form asks for drug use in the past year. At least 3 people tell me that I should just lie and put no. I hate lying and do not think that is right, especially because I'm working toward a Forestry degree and will not be my final dance with the federal government. I've smoked in October. and possible a total of 10 times in the past year. I was an occasional user in college and dropped to sporadic, sometimes going 4 months without touching it since 2012. I want to show I have no intent of continuing and have no negative pressure to. My job and life are more important. What are my chances? Can my current job deny me the promotion or fire me if I don't make clearance? Will an unfavorable rating be told in detail to my current employer? Please help.