jenluckenbach more or less covered everything but there's one more thing you can try. As smart as cats think they are, you can always try psychological warfare.
Cats HATE to poo in the same area they eat. If you lay out a dish of food in all of the "trouble spots" the cat will probably start to avoid them.
Another thing is to use disenfectant at the places the cat has gone outside the litterbox and disguise the smell COMPLETELY otherwise it might prompt the cat to go there again.