this isn't my rule I'm just stating it to you since you wanted an answer and now you received it.In that case, when you're giving dawah to non-Muslims you should make sure that you tell them "oh btw, think about it carefully because once you enter Islam you can't leave. If you live in a country governed by the shariah you can be killed for it unless you keep it to yourself". Of course this would be after you finish telling them about the beauty of the religion of peace that is Islam.