I would like to keep our 4 chicks - 5 weeks old - free in our back yard during the day. Problem is that we have a Coopers (?) hawk and a cat that roams the neighborhood. When are they old (big) enough that I don't have to worry about a neighbors house cat? Standard size not Bantams... We live in the city and have a fenced in backyard. Right now I only let the girls out if we are out. They don't even go all they way to the fence. Thanks!