My brother and his buddies have been doing this in RI for years. They search craigs list for old swing sets and other large metal objects and have been building a reef for about 6 years. They are all spear fishers so they hunt this site not fish it. I wish I could get a pic of the entire structure it is huge in about 60' of water. They use old cement blocks and chain to hold it all together. All of them are scuba divers and bring the material out in a boat and put it together underwater. It is quite the structure and always holds fish. The metal rusts pretty quick so they just rebuild as it corrodes.