cat-safe run?

i moved my 7 girls out to their coop on the 17th, they were 5 weeks old (2 buffs, 2 PBR and 3 SLW). i fenced off a small area around their coop, and let them out in the morning for an hour, and when i get home from work for about 2-3 hours. i leave the door open and use a screen door during the day so they can get used to their environment - the sights and sounds. the fenced off run area is about 2' around the perimeter of the coop (which is 4x4). i'm going to open up another 15' of run for them before i give them the entire area. i've got netting over the top, but it isn't secured very tightly. my cat can climb up the 5' chicken wire (2" hex)! i'm worried that she'll get in before the girls are big enough to take care of themselves. they're never unsupervised for long outside because i just can't trust bella. i buried the fence about 6", and one wall is the back of my garage. i need to get some pics uploaded, but i'm wondering how to make the run more cat-proof. the netting will keep out hawks and such, but i live in a residential area, so we don't have too many (big) predators. at what age will the girls fight off / "hen peck" at Bella to scare her off? 4 months? never? any thoughts are appreciated! their full run will be L-shaped, with total area of 170 sf. i want to be able to leave them out during the day, but now that i've moved them outside, i'm terrified that something will happen. it's just not right to leave them cooped up all day...

saturday they were out for nearly the whole day. they were in ecstasy! they rolled in the dirt and fluffed their feathers sending the dirt flying; rolled their heads toward the sky as if they were rolling in the dirt. they all huddled together doing this rolling and fluffing bit for at least 15 minutes. they did it again on sunday! i simply must find a way to assure their safety in the run! i think i'm becoming chicken-obsessed....