Containing Roots

Last year was my first year w/hops and I kept them in pots all summer since we moved half way through. I'm thinking pretty seriously about getting them in the ground for this summer, but am a little concerned that they will take over my yard. What do you do to keep the roots contained in the ground and does it become a big problem or do you just need to cut back the new growth every year that's where you don't want it?
Thanks in advance for any advice.

I had my first year hops in a large container. WHen I put them in the ground this year I just cut the bottom off the container and put the entire container in the ground. I'm thinking this will make the roots grow down more before they grow out and spread all over the place. It may still be inevitable but we'll see.

For anyone interested or that has the same questionsl, I've done a bunch more reading on the topic and I think I have found my answer. For starters, I didn't realize that there was a difference between the roots and the rhizomes. Again, probably common knowledge to many. The roots actually grow down and out to provide stability to the plant while the rhizomes grow closer to the surface and outward parallel(ish) to the ground. I ran across a pdf on the freshhops site that is about hop farming. It sounds like what the author recommends is tilling the soil around the crown throughout the season if you'd like to prevent them from spreading, at least for larger scale farming. In the spring it sounds like you can also till up the soil around your crown area to dig up the new rhizomes from the previous year. I think that this will likely become my method. I don't have a ton of space for my hops in my garden so they will be pretty close together, I'll have to keep on top of it every year to ensure that they don't get mixed together and that they don't spread out of control each year.
If anyone is interested, this is the pdf I ran across: http://www.crannogales.com/HopsManual.pdf
The details on annual maintenance are on page 25 or 26, depending on if you're using the pdf page number or the page number in the document.
If anyone else has any advice on how difficult this annual maintenance is or how to best accomplish what I'm after, I'd appreciate it.
Thanks

Does anyone have feedback on the method that SOB mentioned in his reply? Thinking about the rhizomes growing out horizontal and the roots growing more vertical, the whole plant the large pot method is starting to make more sense to me now. Will the rhizomes not eventually grow down and out of the pot? Do they just stay close to the top of the soil where they can get a bit of sun? For those with experience having those in the ground for a few years, does that method work pretty well for keeping them contained?

the method SOB suggested is great. as mentioned, the great majority of the roots grow downward (some laterally) and the rhizomes are oriented just above the uppermost roots, grow laterally and will eventually turn upwards at some point. in this case they'll grow upward when they hit the side of the obstruction (bucket). really, any type of border or obstruction you can incorporate a few feet out from the crown (4-6 inches deep) SHOULD contain most rhizomes. they are usually a little lighter colored than the roots, and have BUDS/EYES on them. the roots do not and cannot propagate new plants. telling the difference between the two may take some time for some of us. if you spade up the soil about 6-10 inches out from the crown(all the way around the crown) each spring, you'll dig up or uncover any rhizomes growing out from the crown and can deal with them as you wish. planting the initial rhizome vertically will make this task much easier than if you were to have planted it horizontally.