I have a friend who grows M. floridus, C. selloana and a few different kinds of running Bamboo in top & bottomless plastic 55 gallon drums, buried in the ground. He watches for rhizomes trying to grow over the top, and cuts them off.

I'm not sure you have to go that deep. The Bamboo people say 30" is sufficient for root barriers. Others claim that root pruning to 16" is sufficient.

Interesting idea Donn! The barrel would give a nice clump size. Just thought too that it might allow planting closer to tree roots that otherwise might sneak into my ornamental grass' enriched root zone. (ha!)

Without water being blocked from moving horizontally through the soil by the barrel, irrigation may prove necessary though. Smells like an experiment coming soon.

I found a landscape in a nearby town where invasive ribbon grass was planted in whiskey barrels set at an angle into the ground. From the looks of the island planting, this has been around for awhile. Either whiskey barrels provide adequate restraint and slight water permeability, or the grass is hooked on whatever whiskey remnants are in the barrel. Either way, the grass looks remarkably healthy for being kept this way.