We had Cedar restricted first to her kennel, then an xpen, then one room, then three room (sorta great room type space) then limited to the main floor minus bedrooms and the only carpeted room. She had just been given access to the carpet room (about one year old) when we introduced Willow, a mill rescue who was a few months older than Cedar but had little time to house train. We cut both girls back to the xpen.
So far, so good. We havent had many accidents at home at all. We have had issues with accidents at my folks, though, so we know Willow isnt associating all houses with no-no places yet. So we just take it step by step.
Cedar (tri), Willow (blen), & Holly (ruby)