When mine spread, I use a spade, and cut off the underground parts that go beyond where I want them. Or time to dig them up divide 'em and replant portions. That happens with a lot of perennial plants. Be happy that they are growing so well that they want to spread out.

-Babka

Why not dig up and separate them? Keep one where it is and move the one with the spores to a different spot where they can spread, or remove that variety all together? Maybe you know someone who would like them. I gave a bunch to a neighbor who has a very shady yard.

debra

It looks like putting in a barrier might be a lot harder than I thought - so, I may end up just using a shovel to sort of edge-prune them every so often. Or, maybe when the ground is softer, I'll get up the energy to do a barrier.

Whatever I do dig up though, I'll try to find it a new home.

Thanks, people!!

Western sword fern, Polystichum munitum, is a definite clumper, not a spreader, so you don't need to worry about that one :-) It doesn't even produce offsets but if happy in its location, it will reproduce quite freely.