I have been playing all the games I can think of with the hose... or just spraying myself with it.
We fill up a "doggie" pool (it's a kiddie pool from Toys R Us) in the back yard and the dogs walk through it (cooling the pads of their feet and drinking out of it. Emma dips her whole body down in it.
Downside is they can get muddy/dirty if they roll in the bark.