Originally Posted by blink
Or even simpler than Diana's suggestion is a simple standpipe for the intake that sits an inch or two below the surface with a strainer on it.
This is the exact setup of my tank. Intakes are positioned about 2" above the substrate so in the event of a failure the yank doesn't completely empty and my fish all survive.
In my tank I've never had a leak due to having a bottom drain. The only issue I ever had was a failure in my drain valve causing it to drain excessively. The above setup is what kept my fish alive.