Definitely a tricky problem!
I measured this morning and found that I had over estimated. The hole the goats got through was actually 12" x 14" - I have no idea how my horned goat, Nanny got through there. Anyway, I did what Freemotion said and put a strip of wood about half way down so now...
I'm new to both chickens and goats and just got all of my animals within the past month - I'm still trying to figure all this out!
I keep my goats and chickens in the same area and found that I really need to let the chickens have an area where the goats can't get to. I cut a small enough door...