Two areas that need to be addressed are litter box maintenance and litter box location. Litter box maintenance refers to how the box is cleaned. For some cats, it is necessary to keep the litter box scrupulously clean. This may mean changing the box daily, or at least removing feces every day. The choice of litter material is important.
Some cats prefer a plain clay litter material without any odor control matter added.
Other cats may prefer fine clay litter materials that clump and allow for frequent, easy litter box cleaning. If the same litter box has been used for several years, discard that one and get a new one. Another factor that may need to be changed is the type of litter box. If the cat has always used a covered litter pan, a change in body composition or mobility may make removing the cover important. If a cat has become overweight, it may no longer fit comfortably in a covered pan.