I am looking for a cone shaped nesting box predator guard that attaches to a 4x4 post (like an upside down funnel about 2' wide). I have 2 blue bird houses attached to the 4x4 post and want to prevent predators from getting into the nesting boxes. We already have blue birds on one side and swallows on the other, and I am hoping to protect them. Any idea where I can purchase one? Thanks.