Recently, one of the pros from King Plumbing Heating and AC recommended I get an inexpensive water sensor alarm. I'd never even heard of such a thing, but they do really exist. I couldn't find one at a local store but I found it online and here it is: A Zircon Leak Alert Electronic Water Detector. If you order one, pick up a 9 V Battery for it too, because you'll need one and they are not included.
It's a piece of cake to set up. Just install the battery and place the Leak Alert anywhere near potential water problems. It will sound an alarm loud enough for you to hear if there is a leak. You can order your own Leak Alert Detector for about ten to fifteen bucks using the links below. Pretty cheap water damage prevention if you ask me.