Not to put too fine a point on it, but with only 0.4 acres, you are not "free ranging", you are "yarding". So you will be establishing a perimeter to keep your birds in and predators out. There are a lot of options, depending on how permanent you want to make it. Then there are other factors to consider such as wooded or open. If the land area is wooded, and there is a canopy of trees that extend over the property line, then those create an avenue for raccoons to simply walk over the top of your fence. They go up one tree outside your fence and come down another inside your fence.
Assuming no worries there, the best solution I can think of to enclose that much area in the most secure way is electric poultry netting. That assumes a house or coop area that is not secure at night. Not closing the door to Coop Fort Knox.
I don't know if you can make that 100% secure to all comers, but electric poultry netting would be the best place to start. A physical and mental barrier to keep birds in and predators out.