Anchors, of course. In Jack's case it is just a blue bag of rocks tied to a rope but it effectively kept him from "sailing" away at a recent barbecue at the lake.
I started out trying to keep him on a really long leash and let him run up and down the dock and in and out of the lake. Not a great idea I found after nearly decapitating my unsuspecting brother-in-law—Jack took off after a bird with me in tow and his leash knocked the poor guy, and his beer, out of his chair.
Now I have an idea of what to do this winter. After describing this anchoring of the dog scheme to another U.P. dog lover, she told me this is (sort of) how sled dogs are trained to pull. So this winter neighbors beware...I'm thinking Jack, a harness, a sled and I'm set to zoom around town the easy way.