My ROPS are too tall to drive in the garage, so what I do, is always, always, always, back the tractor in.
That way, at least I am looking backwards and there is a CHANCE I'll notice the ROPS are up !
(if I drove it in, nose first, I'd have to remember they're up....at least this way, I am looking backwards)
This morning, before snowblowing, I added paper "signs" that hang off the inside of my garage door, that remind me to fold down the ROPS. With the garage door up, they hang down, nearly at eye level as my garage door is not as tall as most.
They aren't huge, so there's no guarantee, but at least there's always the CHANCE I'll see them.