My cat like to take a running jump off of WalkingRocks shell to get to the top of our fence... when she was a fressh kitten she tried to get him to play but his constant lack of interest just drove her to use him when ever she feels like it at a highly moble stepping stool. I once found them curled up together under the basking lamp(when he had one) in his house... WalkingRock looked quite put out by this turn of events but Squirrel, like most cats really didn't care what he liked!
I wouldn't trust cats or dogs. I've had my dog for almost 11 yrs and and my turtle for 12 and I would NEVER let her near my turtle. Cats and dogs are unpredictable. Can you imagine if your cat swiped at your turtle and caught him/her with a claw?..I would never trust it, no matter how docile your cat or dog were. I would always err on the side of caution.