rocks I got from the woods, they are just a shale/slate rock. They are normally easily formed into little piece. You can use round rocks too, which will give it a different look. I don't suggest trying to make the wall waterproof. But when you lay the dirt behind the way, run a thin layer of gravel between the wall and the dirt this will help stop soil leaking out from behind the wall.
The toad gets fed mostly chopped up worms. Though when had to leave for a week I moved him to a 10 gallon bin on my floor. The crickets I bought him would attempt to drown themselves within minuets of being placed in the paludarium.