I know I have one too. Was assured it would be "out and about" when I bought it, but it spends its entire life in my rock work. Every once in a while, I'll spot a claw sticking out but that's about it.
I upgraded tanks nine months back, and still never saw it. Last spotted when I set a trap to remove some nuisance sally crabs last summer. Still like the idea that it's in there, but I'd love the opportunity to take a pic like that. Beautiful invert!