"Sunflower" , if you're frightened, you
can be frightened, it's okay:

Depends on the grass species. Bermuda will survive and bedevil you with new
runners sent up for years to come. It will sometimes survive spraying with
Roundup too. Even "extra strength" Roundup. It is evil.

Aye, Johnson grass as well. Putting down cardboard overlapping and
putting dirt on top of that or several layers of newspaper (thick, not
a thin layer that a runner will easily poke through) might handle
bermuda, but I haven't tried that. I actually intend to try it soon
though as I want to terrace a hillside and I also wish to do it the
easy way. The bermuda is rampant here and so is the Johnson grass,
although I have been slowly but surely eliminated the latter since I
moved into this house.