I have grown it for years. When I first started I built a two foot square raised bed out of 2X8's. Placed it on the ground and pinned it down. Filled the raised bed with good soil and plopped in the root. Has been there growing in a controlled situation for years. Each year, as others have said, I dig it up, cut everything off except a couple pieces with eyes. Plant those back in and forget it for another year. When in full leaf, it is possible for wind born propogation, but I have never found more than the occasional leaf sprout, here and there, outside my raised bed. When I do, I just reach down and pull it up. If I keep my eye out for them, I get them before they form a root system. I have never had the reckless spread that I have heard about. Not that I doubt it. It sure could happen if you disc it up or tilled into it or were growing in an open garden. But this little raised bed, right next to my garden has been a good shepard for many years. I think the potters would work well too. they just may need a little more watering, because potters tend to drain and dry out a little faster than raised beds or in the ground situations.
Also, someone mentioned not liking vinegar because it made things too wet and runny. I found that timing the application of the vinegar was key to controlling the hottness(if that is a word) of the end product. After timing the ground horseradish, I flood it with vinegar. After it has done it's job, I press the vinegar out and either reuse it, if I am making a later, hotter batch, or dispose of it if I am done. The result is I stop the growing heat, but still have damp, not soppy completed product.