Thanks! I just finished putting in my emergency shut off float swithes. I placed one in the sump and one in the back part of the tank where the water level is lower. If I loose siphon, the water level will rise in the back part of the aquarium, trigger the float switch to shut off the return pump or if my return pump fails and my sump starts filling up then the pump in the back of the aquarium will shut off and lower the water level below the overflow.
Tested it and it works. Here are some pics.
Back of the aquarium - 
The sump - 