How do I stop birds from building a nest on our front porch?

Last year birds built a next on the arch on our front porch. It was fun to watch the baby birds hatch, but the bird droppings all over our entry way porch was a constant mess. We took the nest down after the birds flew out of the nest. Now they have returned a year later and are starting to build a nest in the same place. I have a green rubber snake and a plastic bobblehead owl on right under where the nest is being built. The birds are totally ignoring it. I've even moved them around daily. Any suggestions?