They seem to be un-imprisonable, as far as I see. They can drain magic and decay matter. So that covers.... everything. Eventually, they'd get out of any ward or prison you'd devise for them.
Can't you keep them imprisoned in a ring of Patronuses?
Sure, if you're willing to devote dozens of people to 'round the clock duty, forever. Better hope none of them has an off day wherein they can't maintain the prerequisite happiness.
Now, if someone created a Charm that would replicate the affects of Patronuses w/o the need to constantly maintain it, or (Deathly Hallows movie pt1 spoiler) Hzoevqtr'f Cngebahf fuvryq was canon, or at least MOR!canon, that might be a different story
Update: Discussion has moved on to a new thread.
After 61 chapters of Harry Potter and the Methods of Rationality and 5 discussion threads with over 500 comments each, HPMOR discussion has graduated from the main page and moved into the Less Wrong discussion section (which seems like a more appropriate location). You can post all of your insights, speculation, and, well, discussion about Eliezer Yudkowsky's Harry Potter fanfic here.
Previous threads are available under the harry_potter tag on the main page (or: one, two, three, four, five); this and future threads will be found under the discussion section tag (since there is a separate tag system for the discussion section). See also the author page for (almost) all things HPMOR, and AdeleneDawner's Author's Notes archive for one thing that the author page is missing.
As a reminder, it's useful to indicate at the start of your comment which chapter you are commenting on. Time passes but your comment stays the same.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: