ok. this is exaclty the way i set up my fuge. first off i had to raise the fuge a cupple of inches for it to work. ive actualy had a flood but not because of the fuge(the filter supplying the fuge) but to be carful i have 3 overflows that go back to the fuge, that way if one gets pluged the others will still work. i found that only one will feel like its working but they all work. also as an extra precaution to floods you could put the pump to the fuge high up close to the top of the water level. that way if water did start to flood, it could only spill enough water to drop the water level back down to the pump and only really spill 1 or 2 gal
(it will also help keep oil slicks from forming on the top of the water)
hope this helps.