There used to be a "if you visit the area" post with details on rentals and places to ride, but I am not sure where that thread is.
For higher end bikes, Roaring Mouse and Big Swinging Cycles both have good bikes. Basically, you are renting a demo bike and will pay some $70 a day for it.
For a cheaper ride, one of the Blazing Saddles locations has Ok MTBs (most sites rent hybrids for the masses, but one site has true MTBs and road bikes). I think it is the Columbus Ave site with the Ok bikes.
Another option would be to go to Passion Trail Bikes in Belmont to rent a bike and ride from their shop to Waterdog. You could do this car free by using CalTrain to get there.
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