If you think outside the box there are perhaps several solutions.
HVAC units in an attic typically sit in or over a pan. This pan normally has a drain and a high level switch. The unit is suppose to drain condensate through a loop seal. Algae and gunk can grow and stop up the drain. Then the pan starts to fill. It too has a drain but can also get plugged. As the last defense against flooding the pan high level switch is wired to either stop the compressor or stop the whole unit.
I guess a pan switch could be placed in a WH pan. Then it could be wired to an alarm. If action is desired rather than an alarm then the switch could control a solenoid valve on the cold water inlet (closes on loss of power). On high level the valve would shut. Of course if you are out of town when the WH starts leaking and the leak is in the bottom of the tank, you can slowly lose a whole tank over time. And with mineral content in the water the solenoid should be cycled say monthly. A solenoid never exercised would likely not work at the ten year mark when a leak occurs.
The Marathon is a fiberglass tank with a polybutylene inner liner and polyethylene outer jacket. No steel, no anode, no rust. http://www.marathonheaters.com
They are not cheap; but probably cheaper than water damage from a failed WH. Cheapest source I know is http://www.chec.coop Tank failure possible but not likely. I guess even anvils fail or wear out eventually.