Phil Dunning suggested these, when the (outrageous) proposition that his monster grinding wheel be used as a mooring was put to him.  Finding a boulder around Franklin is not an issue, but attaching something to it so that it can be useful is.  Laurence Burgin from Franklin Marine came up with the solution:  a length of chain, some marina bolts, a pot of epoxy and a VERY big drill.  Thanks Laurence.