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I used to highly recommend duct tape to "contain" young'uns until I read in the paper a couple of years ago about a couple of ladies who followed that route and ended up in jail. Now I recommend Velcro.
This works great for exterior containment to at least 2 years old. My 2.5 year old learned how to unzip the zipper the other day though and my heeler decided he didn't like the netting!