There are tons of suggestions in the Predators and Pests folder. Search for 'proof' or 'predator' and you'll get tons of hits.
Chicken wire is good for keeping the chicks IN but not so great for keeping other critters OUT.
Burying wire out from the base of your coop/pen/run will help deter digging animals. Using hardware cloth will make it harder for possums and coons to reach through and grab a chicken while roosting.
Cover the top of the run to deter climbing raiders and birds of prey. Some here also use electric fencing around their coops.
Good luck!