For size, I'm having good results with Ph. atrovaginata. My two-winter planting had 75% leaf burn and put up several 8 foot culms. The diameter of rhizomes escaping the area suggest 5/8" diameter culms next year. It doesn't put up as many shoots as aureasulcata or bissetti.

Go with the 24 inch barrier, leaving it an inch or two above ground level to prevent jumpers. Digging the trench will be a huge effort just for 24 inches, going deeper than that would be insurmountable without heavy professional equipment. Most runners don't dive deeper than 10 inches. Also make sure you overlap your circle heavily; I've had mine get in-between the overlap.