Since my dog, Mona, has proven she cannot be trusted with chickens my husband wants to build them a large run. His plans are for a large square, 25' each side. The coop will be in this area, but will be raised 2 or 3 feet off the ground so they can go underneath. We have 9 chicks now (white leghorns), but want more in the spring. I don't want them to be crowded, so how many chickens can happily live in an area this size?