The main problem will be when it is time to take a division. It is nearly impossible to divide bamboo inside such a container since the woody rhizomes move to the outer edge of the container and then circle. The pressure and friction they exert make extraction a real pain. I'm not saying it's impossible, but I guarantee you will butcher the rhizomes and the container, and use your full vocabulary of swear words several times before you're done. If you can get the container back out of the ground first, and then destroy it to get at the root ball, the process of division won't be so hard. If this sounds like a pain, and you decide not to divide it every so often, then the root ball will tend to start choking itself off, and the bamboo will start looking worse and worse.

kudzu knows what he is talking about he is a very wise man I have made this mistake more than once. Now I'm facing destroying my barrels but if you can you should just plant in the ground and rhizome prune it to keep it contained I wish I would have. But I was experimenting to see what I could get away with leaving it outside in a protected area.

Thanks, I see what you mean...my main reason for wanting to contain it rather than prune it is because I plan to put it in a garden near other defenseless plants...I'm trying to decide if the barrel idea might be worth it to have a few seasons worth of relatively carefree growing and then just destroying the plant and starting anew...
Hmmmmm, what to do....... Thanks again!

The metal will rust and the bamboo will break thru it. Plastic will last much, much longer but only the part that is not exposed to the sun, so you need to heavily mulch the part that is above ground (and you DO need to leave at least a couple of inches above ground so the rhizomes don't jump over the top). Why not just use "Bamboo Barrier"? You can order it thru BambooHeadquarters.com.

If you're wanting to have easy access to divide/propagate later here's an idea. I found that the runner bamboo I had planted in upright 15 gallon pots and set on the ground had put down feeder roots into the ground but it was too deep for the running roots to go. I easily knocked the pot over (feeder roots break easily), cut the plastic pot and divided. If you want something nicer looking maybe you could semi-bury a nicer pot that was at least 2 feet tall into the garden.