What Batman Really Thinks Of Every Gotham Villain
3. Ra's Al Ghul
You can kill Ra's, and he comes back with a Lazarus pit. You can destroy his plans, but he'll come back with more. After all, he's been around for a couple thousand years, he's pretty used to this whole shtick.
Unless you outlive the head of the Al Ghuls, you simply can't beat him - and even if you did, you'd still have to deal with Talia.