This is what I think I'd do (it'd be much easier done while installing the tank, though):
I'd install the tank in a pan. You'd need to basically plug the outlet so it can hold some water. I'd also install a WAGS valve www.wagsvalve.com. The valve will shut the water off if it detects 1/2" of standing water. If it is a gas WH, it can also be set to disable the gas valve. If installed by a certified installer, comes with a big warranty against leak damage. Made by a well-known manufacturer.
I think I saw a pseudo pan that you can install afterwards that glues to the floor to contain the water instead of setting the WH into it. Probably doesn't work as well, but might work for you if you're not willing to do the work to insert a pan underneath.