Usually the siphon in the tank is only a couple of inches below your water line and the sump should have enough space to hold the extra water in it the event of a pump failure. If you have PVC
piping you can install a check valve as well, although I haven't found a great check valve though that doesn't have any metal in it.
"What kind of name is Poon?"
29 gallon hex, canister filter, too much live rock, two powerheads. Tank setup June 2012. Two clowns, fire shrimp, 2 chocolate chip starfish, 3 snails