We have 2 guinea pigs: a long-haired girl, about 4 years old named Theodora and a short-haired boy, around 1 year old named Sylvester. They are caged separately, since we don't want any accidents. We also have 3 ferrets, who are kept on a different floor of the house, but when they are brought near the guinea pigs, they have never shown anything but just a little curiosity. They've never been left alone together & never will. We would like to construct an outdoor cage for our pigs since the weather is breaking, so they would have more room to run. My son purchased untreated Cypress Mulch for the bedding...is this safe for them?