Are there any features of cookers that make them rodent resistant?
The hose that supplies the gas is probably not part of the cooker itself, but a separate part which can be swapped by an armored one. 

Manufacturers don't have a rodent-resistant label, what you need to know is whether chewable materials are part of the construction. The best way to tell this is to lift the lid and look at the supply to the burners. Generally these will be metal, not materials like rubber or flexible plastics.