Our whole kennel facility is concrete and cinder block construction. The building is a metal clad structure. In our experience, concrete is the only material that is able to be consistently cleaned while giving us decades of service life. Other materials are subject to degradation over the years by chewing, rotting, etc. Also, any porous materials such as wood are subject to retaining smell and disease. The outdoor exercise pens are heated concrete as well to facilitate cleaning all year including the winter months. The warm concrete has an added benefit of keeping the dogs feet warm in the winter while outside running around.
Outdoor exercise pens must be able to be washed and cleaned. No matter what anyone says or does, the fact of life at any pet boarding facility is that pets produce a lot of waste. If you cannot clean it up properly, it builds up and becomes untenable. Gravel and dirt pens will retain every single urination in the ground and will eventually lead to smell and unsanitary conditions. We have 6000 square feet of exercise pens outside sectioned up so we can put quite a few dogs out at once and clean the inside while they run around. We scoop the poop after each group and pressure wash the whole thing into a single drain every day. Because it is heated concrete, we wash it EVERY day, even when it’s 30 degrees below zero.