Lilly just went up stairs
And right as I was going to bed too
I have the perfect solution to this: get rid of the stairs. If there aren't stairs, she can't go up them!
Then we're faced with the problem of needing a method to get up to the next floor that's usable for humans but not dogs. One of my first thoughts was a rock climbing wall, but not everyone's great at rock climbing. What about an escalator activated by weight--things heavier than Lilly will activate it and take you up to the next floor, but if lily stands on it it won't work. This also should work for pretty much anyone because it doesn't require any exertion or specific physical capabilities
Hmm. Then we encounter the problem of children who are dog-weight needing to go places, and also escalators can function as stairs even when they're not working
Okay. So the escalator stairs are going to need to be comically large to prevent Lilly from being able to climb up them when they're not in motion. This doesn't solve the child problem but we'll think of something.
Maybe we take a page out of kotlc (metaphorically) and we make these comically large weight-activated escalator stairs required a little DNA strip, to prove you're not a dog and are, in fact, allowed to use the stairs.
You could input your heaviest dog's weight into the escalator and then it can be tailored to your specific family's needs, as anything over that weight would automatically not be a dog and therefore would be allowed to use the escalator. Then, only those who weight less than the dog (likely children) will need to use the strip, and kids love licking things so this is a win. And if the child is too young to use the strip, then they probably shouldn't be going up the stairs alone, so it's fine that they can't activate it.
There. I think I've solved your dog going up the stairs problem! Now we just need to invent this and install it in your home. This is definitely going to be super easy and not at all the most ludicrous way to solve this problem