I don't have a boink problem with mine. The top of their cage is probably 18" up. I guess they learned early on (when they first got the cage) that the top didn't give. No one got hurt, but they learned to stick to the ground!
They normally just run around when I go in there, usually all over my hands. Now if my son gets in their cage, that's a different story. But all the animals are afraid of him!

