This idea came from a sweet lady who lives down the street from me. She told me it works great for keeping the rain and her dogs out of the beer she uses for slug bait. Beer, by the way, is a phenomenal slug bait! See more about it on THIS POST.
Just save some half-gallon milk/juice jugs. Cut off the top and handle.
Shove it into the ground over your sunken beer tub. Now you have a covered “Jacuzzi”… (you’ll have to read THIS POST to get it)