The surfaces previously noted should suffice. If the enclose is not too large, the expense should not be an issue. I own 3.5 acres, with two kennels on my property, each measuring 40 feet X 60 Feet. I stopped keeping my dogs in the kennels, as they scale the 6 foot chain link fence and constantly scavenge in the surrounding state park for deer carcasses. However, I have trained all my dogs to use the enclosures to deficate in. Training was quite easy and took only a short time. They rarely go outside these enclosures and when they make a mistake, it is in the general proximity of their enclosures. Consistency in training is of the utmost importance. I clean the enclosures regulary, which is a must. Each dog possesses a unique personality. Some of the dogs I have owned, relished in the scent of excriment and appeared stimulated by such, while one dog I owned absolutely disdained areas containing dog feces.