It is quite invasive if it likes the situation, not sure I'd risk it on a rockery. I've certainly grown it in the border, usually in 'difficult' situations (not full sun for instance) and its not been a major problem.

I might relegate it to the beds under the beech tree then. They are corms and I will try to dead head it: if I remember. perhaps the squirrels will dig them up haha.

I don't recall our resident squirrel being in the least interested in the corms - but maybe that's why it didn't spread out of control!