Question–can I stop comfrey from spreading with some of these?

I planted a small bare root of comfrey a couple years ago around some fruit trees and, well, you know the rest of that story. I now have it everywhere, and I don’t necessarily want it everywhere! If I enclose the area where I do want it with some of these steel edging strips, will they be deep enough to contain the roots from spreading? How deep do you think the barrier would need to be to prevent the comfrey from spreading? Thanks in advance!