What kinda chain should I use to moure my boat buoy? It will be underwater all the time.?

I have a pontoon boat and want to leave it in front of my cottage on a upstate NY lake. I will drop a heavy weight to the bottom of the lake, but what kinda chain should I use to attach to the weight and then to the buoy? It needs to be strong and mostly rust proff. Also what chain will work best when rubbing on another metal article (the weight)? I guess I need to know what is the strongest chain out there for me to use and not worry about breaking after a few years of underwater use.