You pretty much need absolute fort knox. I have learned this the hardway myself. When my dad and I discuss this, I used to say, "naw, a racoon can not climb 5 foot streached horse fence. And even if they did, they are not going to scale the coop wall 5 feet straight up through a knocked out window. There is no way the oldtimers spent all the time and energy bullet proofing the coops. We've gone a month without a casualty. Besides the chickens love that open window"
He said, "you may be right, you may be wrong. Do what you think is best."
Over the last 3 days I have lost two hens (ouch). Heads missing. Today we bullet proofed the coup. (for the 5th time). We also probably annoyed the neighbors a little bit with some after hours activity.
You must do both. Coons are too capable, too greedy and too fearless. Possums are almost as bad.