Has anyone ever heard of someone striking an unspent Cartridge with your shovel and the round actually going off? Has anyone ever died from this situation before?
The setting a primer off with a shovel is about as likely as being struck by a meteorite. I won't say that it can't happen because crazier things have, but the chance is very, very low. As for the rest of the cartridge, you could beat on it with a hammer, run it over, cut it in half with a bandsaw, whatever...it's not going to go off. (That shouldn't set a primer off either, really.)
If you did manage to somehow set off an uncontained cartridge, it still won't be particularly dangerous as others have mentioned. Your biggest danger would be a piece of flying debris hitting you in the eye. That having been said, I seem to recall Julian Hatcher mentioning in one of his books (probably Hatcher's Notebook) a curious case where a woman was killed by just such a thing. Apparently while loading some wood into a stove, she inadvertently dropped a cartridge in as well; it exploded while the door was still open. If memory serves, it was the casing or the primer that killed her, not the bullet. Hatcher mentioned it exactly because it was such an unusual thing, but that was pretty much a one in one million sort of thing. So yes, this can kill someone and apparently did kill someone once, but that's the only incident that I've heard about and I used to deal with this stuff for a living, and it happened before my father was born. It's certainly not a common thing.
I once observed a .50 BMG cartridge detonate in someone's hands...true story, and I'm willing to tell it if anyone is interested. There were probably some soiled drawers but no one was injured. As you probably know, this is a very large round and it was literally sitting in someone's hands when it popped. I'm not going to say that such a thing would absolutely not hurt anyone (and I'm a bit surprised that this person wasn't hurt), but again, no injuries at all, and there were a few people in close proximity when it happened.
tl;dr version - don't worry about it.
EDIT: this applies to conventional bullets only. The moment that we're dealing with anything explosive - cannon shells, grenades, etc. - all bets are off. They're quite safe these days when they're in good order, but pieces of ordnance that have spent a few decades in the ground likely aren't in good order and the fuzes weren't always all that safe back then. Hitting something like that could very well set it off and kill you. This doesn't happen frequently, but it does happen. If you're not detecting on an old battlefield or a former training site, this shouldn't be a concern.
