I use a fanny pack worn around front, too. Works well for a small camera.

You might take a look at these straps:

http://www.upstrap-pro.com/

I use these on my cameras at work. They *do not* slip. I can carry a camera over one shoulder all day long, and it never slips. I have carried cameras while hiking in this manner, too, and it works even over a pack shoulder strap.

You'd probably want the RF/DC model for an S3 camera. The SLR straps are huge.
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--Ken B