Depending on how large your fake grass covers and how often your dog or other pet uses it as their own personal toilet, you need to wash the surface down with water. A hose or bucket is fine and monthly should be enough and the number of times it is used as a pet toilet, you will need to hose it down to keep on top of the smell. Unfortunately, washing in water (or even vinegar) only temporary masks the urine smell. So it is recommended to use a professional fake grass cleaner in addition to hosing/washing.