We were given a NHR hen by a neighbor. She had full range of the backyard and vegetable garden and so did our tortoise who wandered into our backyard one day. Never got a photo of the NHR but here's the tortoise which we found at the bottom of our pool several times. We used to joke that she was a water turtle in her other life before becoming a tortoise! The darned thing never drowned and we never knew how long she was under water before rescuing her. The pool was more dangerous to her than the chicken - the chicken was too busy running up and down the tomato rows eating horned worms and other delectable bugs.
The Persian cat never bothered the tortoise either.
This is the pool the tortoise would go diving into. It's almost like she was driven to dive into it. She had her own water source but sinking in the pool was her thing. The kids were always finding her in the pool or her trying to dive into it. We moved away 3 yrs later and she was still alive so we gave her to a neighbor who had a male tortoise and wanted to try breeding them.
Everyone's family pets are different so you'll have to determine how they interact with each other before leaving them alone. Tortoises, at least ours, was a Houdini digging herself into/under things in the yard. Ours tried to climb the wood gate. Silly but amusing creatures. Tortoises have a wonderful defense mechanism to hide their head and limbs inside their shell so if our NHR ever had any interest in the tortoise there was no evidence of injury to her.