I agree with John on this, raccoons will go to considerable effort to get something they want. I have seen them rip through .25 inch plywood to gain entrance to a chicken house full of chickens, chew through plastic rubbermaid bins to get at the dry dog food inside and and tear a hole through chicken wire to get at turtles in a covered outdoor enclosure. I don't know if they would go to such effort to get at toads which would not be noticed quite so easily, but they are really rather strong animals for their size and should they decide they want to get in badly enough they are probably quite capable of doing so.