I have two bird baths that attract plenty of birds which is lovely. After decades I've noticed that the soil around the birdbath smells of guano from me dumping out the water when I clean it. Can you tell me how I can get rid of the smell and prevent it from coming back? The bird baths are between arborvitae so shaded and lots of tree roots limiting the amount of plants that will successfully grow there. I do have some wild geraniums that are Reluctantly growing I've purchased activated charcoal because I read that would be helpful but I don't know how to use it. Should I scrape away the existing layer of soil and put down more soil or put down something else like a mulch of some sort or sand and mix that with the activated charcoal? Or is there a better way to handle this? Thank you very much for your help.