To keep algae growth from your bird bath drop some pre-1982 copper pennies in. I have what I would call a normal size bird bath & I use 7 pennies. The reason for the pennies being pre-1982 is that before that year, the pennies contained copper, a natural algicide.
Glued pennies to the side of my square foot garden bed to keep slugs away. Slugs and snails won't cross copper. * pennies pryer to 1982 which were made of 98% copper. The pennies after 1982 are primarily made of zinc with a thin layer of copper about 2.5%.