The following article appeared in the Detroit News on 8/31/02. I thought it a valuable article and its one I agree with totally.

Dear Dr. Fox: When I adopt my new puppy, is it possible to train him/her to something similar to a cat's litter box? It sounds impossible to me, but someone said that "someone was able to do it!"
-- P.M., Greensboro, N.C.

Dear P.M.: Some dogs have been trained to use a litter box like a cat, but I don't advise trying it, since failure, stress and distress are the usual outcomes.

Some feline dogs sometimes take to a litter box, learning to urinate there. But all dogs need to go out, not simply to evacuate, but to enjoy sniffing and exploring the neighborhood. It's an important social activity for dogs -- both male and female -- to urinate outdoors and to investigate the spots marked by other dogs.

After defecating, dogs will often mark the ground, as after urinating, by scraping the ground with their feet. This signals to other dogs where they have made a deposit and may indicate their size and strength.

So, for psychological and behavioral reasons, I am opposed to attempts to train dogs to evacuate indoors. It goes against their natures. We need to set limits on how far we go in trying to make animals fit into our lifestyles and often unrealistic expectations.