Have you ever thought of sharing your faith in private, one on one with people who are interested? I myself am Christian, and the school I teach at know it. In the class I do not promote Christianity because it is not my job. I was hired to teach English, and that is what I do. Outside of class I've had people ask me what I believe in and I do then open up to them as to what I believe. I've even had people ask me to give them my bible, and I do because they want one. I've found that those who approach you are the ones really interested, and the vast majority of my students are not. You are thus doing your job and sharing your faith. You can then stay at your job longer and can reach people. You are really setting yourself to be a target for the PSB.