Wow! I guess when you planted the peony the toad took the opportunity to dig a hole in the softer ground. I would fill the hole trying not to leave any air pockets there and cover it with some pebbles or small stones to make it more difficult to dig for a toad. Replanting a peony in another spot is also an option, just make it as fast as possible. Would try to keep the toad in the garden as they eat slugs and quite beneficial. May be digging a small hole nearby and placing the toad there will help?
