Thats kind of the idea i had in mind next.... either that or taking him to the lake and throwing him out of the boat and letting him swim for a little bit....
I dont think i would try the lake thing.. Start small, if he figures out he only has to a go few feet to hit dry land he may learn if hes gotta swim a while it may make your problem worse.
This is usually the idea i get when im pissed at him...
But we are fixing to start hunting some islands out of the boat, so he better learn quick or he will be in the lake with his floaties on....