An expression based on the expression "that ship has sailed," which is when an opportunity has passed you by. One uses "that ship is in my harbor" when one manages to grab the opportunity.
Friend 1: Do you think Matt hooked up with that girl last night?
Friend 2: I don't think so. Anyway, that ship has sailed..
Matt: (eavesdropping..comes in wearing leopard print robe) Nope. That ship is in my harbor.