bulletproof

(adjective) perfect, foolproof, unable to fail

Example Sentences:

I’m going to call my boss and pretend to be sick. Then you and I can go to the beach. He won’t see me there because he’ll be at work. It’s bulletproof!

The bank robbers thought they had a bulletproof plan until they were caught by the police.

Media:

Similar idioms:

1. speed off
2. pick up line
3. epic fail
4. take off
5. when hell freezes over
6. not a hope in hell
7. caught with your pants down