Cypress mulch doesn't mold fast. I think he is mistaken. That is actually one of the best parts of cypress mulch. You can keep it wet and it won't mold or get musty. Make sure you get the 100% cypress and not a mix.
Gravel isn't ideal. It has no way to hold humidity. If it's a small enough gravel he might even try to eat it, which is not that great for him.
Gravel isn't ideal. It has no way to hold humidity. If it's a small enough gravel he might even try to eat it, which is not that great for him.