Law enforcement and natural disaster response teams are often largely dependent upon the help of rescue dogs (or search-and-rescue dogs) to find trapped or lost human beings, or sometimes, in the worst cases, corpses. The most common breeds favored for this kind of work are Burmese mountain dogs, Saint Bernards and, last but certainly not least, Labrador Retrievers. The successful training of a Labrador rescue dog in particular is dependent on several factors, including the dedication of the handler, and the disposition of the dog.
Basically, dogs do not want to soil the areas where they sleep and eat. Additionally, dogs are able to develop habits regarding where they would like to urinate and defecate. For example, dogs that do there business on concrete or gravel will prefer to do their deeds on concrete and gravel and not grass or dirt. You can use these instincts to help train your dog.