i put mine in 4 feet of water and my 4x4's were 6 feet i believe.....i made somewhat of an a frame to support it. all the wood was extra that came from my neighbors deck, so i put about $10 worth of screws and $50 worth of pvc into it....... best bet is to hit up your local dumpster at a construction site and improvise...
(i know you guys are probably sick of this picture, but it serves its purpose)