I know this thread is almost a year old, but I've been thinking about doing this this summer. Is it easiest to run a sponge filter for something like this or is a pond filter better? Also, I'm rural, I know raccoons and opossums are likely to be a problem. Along with birds, foxes, and maybe the coyotes. What's the best way to protect as well as you can from some critter deciding it's easy picking? What are reasonable time frames for keeping them out? Assuming mid April though early/mid September maybe? Thanks for any thoughts.