Anything you own will eventually get scratched. Past bracelet scratches, mechanical watches are rather hardy - unless you're buying something particularly rare and complicated the standard ETA and Seiko movements you'll get in most brands (as well as the house movements of major brands such as Omega and Rolex) will handle physical shocks just fine. I don't exercise wearing a mechanical watch, but that's as much due to sweat and weight and tracking heart rate as any risk of damage.

You can get comparatively affordable mechanical watches that are sufficiently shock, magnetism, and water resistant to do anything normal people will do in their lives. If you're an underwater welder, astronaut, EE professor, or other career with esoteric risks, obviously do your own research and maybe just buy a GShock.