There's probably a lot of other good apps out there that you could use, but personally I use PartedMagic. In it, there's an application call Secure Erase, that's what I use to wipe my SSD drive completely.
I had used DiskWarrior.app, that had saved my system a few times when you encounter this error.
"File System Check Exit Code 8"
Both are paid apps but you can find free apps with google if you look hard enough.