I personally dont think it is, cats are such free spirits, and I wouldn't want to do that to them, you dont know the effect it would have on their mental health, and toileting is a concenr, as while he could be taken out in the garden to poo, what happens if his owners need to go out and he needs a wee, or they want to go on holiday. I have actually had this discussion with a friend, and she is of the same opinion with her dog.