Keep cats and birds from stealing fish, as well as lift fallen leaves from the surface of your precious pond, with a bit of well applied pond netting. Herons are cool and cats are great if they're yours, but that doesn't mean you want to inadvertantly provide a feast for them in your fish pond. Fallen leaves can also block sunlight or rot and affect the careful chemical balance of your pond, so it's good to pre-emptively keep them away if you don't want to have to skim every autumn.