The ways to get unenslaved if you can`t get to 10x your enslaver`s pr are
1)restart: Options --> Restart Empire. Options is near the top-right corner above your empire name.
2)ask your enslaver to let you go. Some of them are actually nice enough to do so upon request.
3)be enslaved by someone else (you can not control this one; to attempt to do so is against the rules anyway). If you`re lucky, it will be someone who will set you free.