Smallest hole a chicken can get through?

[BigFuzzball]

Could chickens get through a gap 18cm square ?
Have recently converted my Grandkids old (plastic) garden playhouse into a coop for our 4 girls (soon to be 6 once the 'rescued' battery hens are through quarantine and integrated).
Reason I ask about 18cm is that either side of the house door there are square framed panels that look ideal to be cut through to fit an automatic up/down door on a timer so we don't have to keep going up to put them away and getting up at dawn to let them out...........advice please !!

 

[N3wtpond]

HI all. I'm having similar issues, one neighbor keeps hunting dogs and they have laid waste to our flock twice now. I have a fenced in ared but keep the gate open to allow chickens in and out, into the woods. Does anybody think an 8x6 tunnel made from planking, but with 2 or more 90 degree bends would allow chickens to pass though, but prevent these medium sized dogs getting in because of the bends in the tunnel? Any experience you may have with this king of idea would be greatly apptreciated. Also, is it going too far to register these attacks with local police, just so they're on the record? thanks.