So after a couple years, what the best thing to do? Dig them out, cut the rhizomes back and replant a small rhizome?
Pretty much if they're grown in the earth, after about 3 years it's time to start doing some serious pruning. Certain varieties are much more vigorous than others, but it's always a good idea to dig a trench around them in the third year. You can trim back any rhizomes that are making their way away from the crown and you can keep them in check.
Containers are a different story. I've started a few rhizomes in 5 gal buckets and the roots pretty much destroyed the drain holes after their first growing season (as I found out when I went to move them). In a bigger container like a half whiskey bbl, I'd say dig the whole crown out at the beginning of the third year and trim it back hard. You'll know how much to trim once you get it out of the soil and see what you're dealing with. For the most part, they don't care and will continue to grow no matter how much you abuse them.