Answer: While diatomaceous earth will help some with slugs, it needs to be replenished regularly and may not give you satisfactory control. I have never heard of it being a threat to toads, however, it can be damaging to eyes, lungs and other tender tissues of animals, so you may choose to try something else.
I think you are going to have to try a number of strategies and be willing to keep at 'em if you hope to win the war! The "slug saloons" available commercially work fairly well. These are plastic trays you fill with beer. The slugs fall in and drown. Plastic pie tins also may be used in the same manner.
Another option for the non-squeamish is to place boards, or better yet hollowed out canteloupe halves (face down) in the garden. Each morning, turn them over and gather the pests you find beneath them. This works for slugs, snails, sowbugs, pillbugs, squash bugs, and several other pests.
While mulch is good, it also harbors slugs. You may need to remove the mulch for a while until you can get these pests in control.
Q&A Library Searching Tips