What Can I Do To Stop My Westie From Going On The Floor At Night?

He is house trained and has been for over a year. My 11yr old insists on having him in the bed with her but doesn’t respond when he wakes her to take him out. Instead of waking me he either goes on her floor or in my little one’s room. Normally if I’m awakened by the jingle of his tags its too late. I’ve found that when I simply tell him “no pee-ing on the floor” in a stern tone he won’t do it. He reverts right back to it if I don’t “speak” to him about it nightly.
I don’t know if I’m fortunate or unfortunate that he is really smart. Is there anything I can do besides crate him at night?