I have my mussurana in a similar tank. she would do the same. What i finally did was grab some strips of Velcro, I really wanted mushroom lock but didn't feel like going out of my way. I flipped the back ground so the slots were at the top and velcro'd it to the glass, and made sure I had good bit of substrate against the bottom. Now I know, all over the place people say don't put tape in your snakes tank, so be aware of this. But i really didn't want to go the silicone route. I didn't want it to be permanent, and some times that stuff still stinks +24hrs later. She hasn't gotten back there since, but does give me dirty looks for stealing her favorite hiding spot. A BP may manage to still pry apart Velcro if they're able to get a good leverage on the slots up top.