You can format a DVD as `Mastered` which might work, though that ought to be the default. click here
Double check the DVD from time to time. I have never trusted this kind of `Live` file system for optical media, in my experience one burn goes wrong and the whole disc can be corrupted and unusable. At least with the `session` based format, you can still access the previously burned data. Just personal experience, you may never have a problem with it.