Ultimately I agree with jorb in that level 10 mining should be difficult, even annoying. It's basically the endgame area for resources, and any character mining down there should already have a very significant investment of time, gear and stats anyways, so the idea of having a miner that can actually fight some slimes isn't ridiculous.
HOWEVER, I can think of some ways to offset the difficulty with a balanced cost and make the idea of getting gangraped by 10+ slimes preventable.
1.
A beacon-like system that either attracts, deagros, or straight up repels smiles and/or boreworms. At the cost of the time, annoyance and materials to create a secondary support-like object in your mining areas, maybe we can make buildable objects that prevent slimes from entering. Perhaps some kind of slime repellent can be crafted using various ingredients, maybe even tricky ones like glimmermoss, or some mushrooms, chitin, etc. Boil it all up in a cauldron and create some kind of weird fuel that can be burned on a brazier-like structure.
2.
Another idea that seems more balanced than just a cape would be a ring. Again, maybe some tricky ingredients, can be crafted together, dried in to a crystal of sorts and used to make a ring that helps repel slimes or something. Rings are a huge source of additional strength and a key part of a miners outfit, so perhaps it's more of a balanced trade to ward off some enemies at the expense of what would otherwise be a very significant stat boost?
3.
Another interesting idea would be to make an existing or new cave monster that agros other cave monsters. Much like the network of overworld animals that fight each other it might help to alleviate some underground aggression if there was some sort of failsafe between all the monsters themselves. Maybe boreworms and slimes should fight? Maybe there should be an additional colour of slimes that fight green ones? Maybe a new monster than can be tamed and bred can be tied to mine supports and used as slime fodder, taking the aggression off the player and ultimately sacrificing itself so you can escape.