Depends on which one you have. A Mud puppy (Necturus sp) is a fully aquatic salamander which requires cool, well oxygenated water. A "water dog" is usually a larval Tiger salamander (Ambystoma tigrinum) which will eventually need a mostly land habitat.
(mud puppies you say) I dont keep any but i have some info about them not for tanks but it would help if you knew but you probobly already know
they can grow to two feet+ if u have a big enough tank
they will eat any fish or crustacean they can fit in their mouth so be cautious
-youll prolly want a tank with a couple powerful powerheads to keep it feeling at home but other than that it should be easy to keep id imagine
The larva of several species are commonly called "Mud-Puppies" or "Water-Dogs" (my grandpa called all salamanders/newts "Mud-Puppies". The pix below are adult phase Coastal Giant Salamander (world's largest terrestrial salamander). Notice the car keys for scale...
Are the two foot long critters Hellbenders? I know in China they have Salamanders that are really BIG.
We had a small mudpuppy at one time (Necturus sp.) but my husband left the intake strainer off of one of the filters and that was the end of that
I was mad about that for awhile.
He didn't seem hard to care for. We kept him in cooler water and he'd eat things like sinking carnivore pellets and worms.