Many ferms have deep, spreading root systems. In Michigan I am stuck with bracken fern. Howevr, even though they break off the root when I pull them, it does seem to kill them. I have persistently pulled them and the root has broken off but they dont come back. Just persist in snapping them below ground. As for a rock garden, they will just go underneath the rocks and come up on the other side. Dig down about four inches and snap their roots.

Use grass/weed killer at the hotest time of the day.

try round-up, this seems to kill almost all kinds of vegetation. If you know a farmer they can get some stronger stuff than what’s in the store.

Also you can try cardboard, wet newspapers ( 1/2 inch thick) or plastic as a mulch over top. The cardboard and paper will decompose after a year or so.

Just dig them up almost all ferns will come back at some point but not likely if you get it out of the ground.