Natural control of pests and disease

We seem to have acquired a pair of thrushes and have plenty of frogs, toads and newts. They will help a bit with the slugs and nails but I think we have them because there are so many slugs and snails. I've found several pile of snail shells in the garden but only need to move a compost bag to find a good dozen more hibernating. This reminds me I need to pick up my chrysanths off the ground in the greenhouse else some will not survive the ever present slugs.