It depends what you mean by key cloning. The remotes uses rolling codes so you cannot just record/reply the signal they transmit. Cloning is only possible with physical access to the key, and programming a new key requires access to the vehicle and a master key.
For relay attacks you need to keep your keys in a metal box/RF pouch, temporarily turn off the remote by pressing keys as per Eddie's reply after each time you use it (or when you specifically want protection), or turn off the smart entry system completely from the vehicle's menu system.
As stated above, the NX isn't a big theft target so I'm not aware of anyone installing something like a Ghost immobiliser in one. I know several people use the steering locks, sorry don't know which ones would fit under the seat.