How can I get my dog to stop pooping and peeing in the wrong place?

I used to watch my dog like a hawk, then my friend's neighbor who is a retired vetrinarian told me another way. He said to clean the mess up with paper towels and put the soiled paper towels where you want the dog to go. If she sniffs it praise her, if she goes in that spot praise her even more. It's just a "praise everything" kind of thing. It's really annoying and takes a long time but with my puppy it was very effective. I did this when she was 4 mos to 7 mos including accidents when she couldnt hold it and I was at school.