I know it feels like lying and enabling him is a way to protect yourself, but really it's not. It's a stopgap at best. I once told my therapist I felt like I was trying to stop a dam from bursting by sticking my fingers in the cracks. Pretty soon you run out of fingers.
So, rather than trying to figure out what to do about the "crisis du jour," try looking at the whole situation. In my estimation, it doesn't really matter whether you lie for him or not, because eventually his actions will catch up to him and he WILL lose his job. So, is it worth it for you to lie in order to prevent that for a period of time? Only you can decide that. But, the more important issue is to start to prepare for what you will do WHEN the inevitable happens.
L