Spray the fence black with a small can of
model/hobby spray, use a shallow DOF, which will help blur the fence more, if AF keeps picking up the fence, use MF. Also use a slower shutter speed and pan with the cars, it will help to blur the fence mesh more. Bear in mind, that fence in there to save you, they don't care about it getting in your shots. At Indy, even accredited shooters had to deal with the fence, with the organisers spraying sections of fence black.
When it has been sprayed, it is suitable for color images, but not full glossy images. When it isn't sprayed, and is still it's natural metal color, your images are only going to be suitable for low res newspaper images.