I read a study some time ago (can't remember what the source of article was now) that land based torts and turts understand the concept of ledges and dropoffs better than water based turts. Its not instinctual for them to dive off such structures into water like a water turtle would to escape predators. However, I would be VERY careful using it as a design feature to contain a tortoise. One act of stupidity on the torts part is all it takes for potentially serious outcome.