Britster, we used a slightly unconventional way to gradually begin expanding Nikko's territory that he hopefully didn't want to pee in... We had recently moved, so we collapsed some of our moving boxes, taped them together, then taped them to walls and desks and other places to create whatever extended or oddly shaped "gate" we wanted. To convince him to not chew on the cardboard, we sprayed the edges with bitter apple spray for the first week or so and since then he hasn't bothered with trying to chew on his cardboard "gates." This enabled us to gradually expand his area by six square feet at a time or less, even if there was no conveniently placed doorway to put a traditional baby/pet gate in. We expaned his area approximately once every two weeks or so, but only by these small increments.
From what I understand, the idea is to make your dog feel like your whole house is his 'den' that he doesn't want to pee in.... and if you can expand his 'den' very gradually he may not make as many mistakes. It has been working well for us so far. If Nikko isn't in his "gated" "den" area, he is in our arms or in our crate. And we occasionally allowed him to sit/lay next to us on the couch before the living room was a part of his 'den,' but only under the closest supervision.
Lauren & Nikko