I have a dog that keeps urinating in my bed, too River is a two year old, spayed, Great Dane. She does not have a UTI. She potties when I take her out, and hasn't had an "accident" in the house for over a year. She has urinated on my bed about four times in the last four months. The first time, I understand; I had a new puppy at the time, who still sleeps with me, and she had had an accident in bed the night before. Fortunately, the puppy is a toy breed River, though, has never slept in the bed with me. The third time, my sister had taken a nap in my bed that day. She has urinated on my bed at least two other times without obvious provocation.
A Great Dane does not leave a small puddle My Little Green Machine is getting quite a workout. What can I do to prevent her from doing this again?

PS. I usually keep my bedroom door closed, but a Dane can be surprisingly sneaky