Water-tight flex containing 4 runs of 4# copper, 2 hot, 1g 1N. 50amp breaker in main, 50 amp main breaker in sub-panel and smaller breakers (gfci) to the loads. Will a ground rod be needed or do I tie the ground back to the house panel? #4 is overkill unless it's 3oo' from the source. Three #8's and a #10 ground will suffice for a 50 amp pool sub.