LC,
We have 15 chickens that roam a fenced acre. They haven't hurt the grass one bit-- in fact, they've actually helped it! They eat grubs and other pests, and the poop has done a wonderful job of fertilizing.
They roam our side yard, which is also where we happen to do most of our outdoor living-- it's where our pool is, our patio and grill, our hammocks and volleyball net, so we'd definitely notice if they were tearing it up in any way. They're absolutely no problem at all, except for having to periodically sweep the poop off the patio and pool deck.
I do emphatically echo a prior poster, however, about any garden plantings you want to keep-- you must fence them out, otherwise they'll be toast!