I have a female, fixed Boxer that is six years old that started peeing on the floor at night when we are asleep. I work during the day and she is fine. She has full range of the house and she is never crated. I take her out at 6:30 am, 5:30 pm, 8 pm and about 9:30 pm. I have had her for five years and I need help. The vet said she was fine.
My second post didn't show; so I will re-do it! I see that you did take your dog to the vet first. (Good for you!)
I would start removing her water as soon as she eats her supper. If she doesn't get a supper, I would take it up when you leave for the 8:00 outside trip. We restrict children's water after supper, it is perfectly acceptable to do so with dogs. Several training books I have read suggest only putting water out at certain times each day. But if yours is ok most of the time, see if holding back in the evening helps.
By
09/17/2010
First thing you need to do, especially if she was reliably house trained before, it to see the vet to rule out medical issues! She could be suffering from diabetes or other conditions. Once medical issues are ruled you, you can try removing her water a few hours before bedtime. We do that to children, it is not harmful for a healthy dog.