Are they on a table or on like an aquarium stand? If its a stand i'd add a few pieces of wood to it. Like a boxed off U Shape.  

This would be attached to the back of the stand and not resting on the floor (not a digging interest). Best I can draw this at the moment is attached but if interested I will try to do it better. 









This would also work with a table but you'd need to make it affixable to the wall (simple picture hanging hardware would achieve this, probably two holes, 3 for best result). For this one you'd need also a thin sheet of wood to frame off the front. Didn't draw that.