House train your dog. A dog that is not house trained will do its business all over your house! To prevent this, simply teach your dog not to go in the house by watching him/her closely for the first week.
When he/she goes to pick your dog up, say "No!" firmly and loudly. Then, run out the door to the desired potty spot.
Reward your dog for doing its business. Then, put a bell on your doorknob and teach your dog to ring it when he/she has to go out!