If there are changes in the house that cause the cat stress, litterbox problems can develop. This can include new roommates and spouses, a new baby, a new pet, stress in the family, a move to a new house, etc. In addition, sickness and physical problems can cause litterbox problems. These issues are discussed in more detail in Litterbox Problems . There are many different styles, sizes, shapes, colors and prices of boxes available.
Covers are really for people.
Covers will help keep odors within the box although you may need to hold your breath when you remove the top. Some covers have vents at the top into which you can put charcoal filters to absorb odors. Most covered boxes are made of plastic although we have seen decorated cardboard covers sold separately. Manual, semiautomatic or automatic Manual boxes require you to scoop out the soiled litter. Semiautomatic boxes have some sort of mechanism to help remove the clumps.