Have you considered how this appears from your employer's perspective? I wish my answer was more positive. Honestly, I have let people go for this. I had an expectation at the point of interview and hiring that the employee be honest about their scheduling needs. It seems you want to take without giving. What I mean is that, as I suggested above, you need to come to the table so to speak. If you expect them to make concessions according to your will and requirements, you need to be prepared to make concessions of your own. That may require honesty and disclosure on your part. Others have said you might ultimately have to find another employer. It is quite possible that if you were to disclose your needs to your boss that they will react with compassion and understanding. I have done this as a manager too. I scheduled the individual for shifts that were during less busy times when their not showing was to have the least impact on the business and their coworkers. Remember, they are the ones ultimately being affected. Have you considered this too?