1 6 7 8 9 10 11 12 
You get a huge bang for your buck, timewise, with water play. It's a quick, safe way to completely wear them out.

The rule of thumb is that it takes 1/3 the time to use the same energy swimming (this is for ... current fitness level. The more fit the dog is the harder it is to wear it out (ASK LANCE MACKEY).

Well, yeah. And your own fitness level, as a happy side effect.
A fit dog is a very, very good thing but if the goal is not to get a fit dog but to get an attentive dog this is going to backfire when the dog's energy level goes up because it's fitter.

I disagree. I don't think of exercise (physical & mental) as any sort of a cure for being a suburban BC or JRT. Rather, it's more like insulin. A maintenance drug, the dosage of which may need to be upped periodically. But my situation differs in that I have three high energy dogs who are extremely busy whether fit or fat. What varies is the mood and general tension level.
Winter sucks around here. Plain old cold isn't a problem, but cold, dark and wet is. The three of them start getting on each other's nerves. The fun police effect sets in. Their fitness level declines but they're still all in each other's business and displaying increasing snarkitude. Getting them out and running or swimming their collective butts off provides a better and longer lasting attitude adjustment than any pill.