Bench dogs, round or square?

The bench dog concept is new to me. I just put my wood vise on my work bench. Should i have one or two rows of holes in line with my vise? What are the pros/con of square/round dogs? I can drill a round hole easier.
These look interesting:
http://www.rockler.com/product.cfm?page=10510&rrt=1

Source: http://lumberjocks.com/topics/27184

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