Kuhli are known for substrate burrowing, my kuhlis and my horse head loaches haven't had the same issues with getting trapped in my decorations as my clowns and yo yos, but they are known to disappear into substrate for days at a time... Kuhli completely disappear, the horseheads will poke just their eyes and long nose up to the surface- but I use sand that's made for sifting bottom feeders, there are a couple places that I have seen them kept in gravel, but never for too long because they get bought up pretty quick. I honestly am not 100% on success with rounded river pebbles- keep me posted, it's good info to have...