…it is hard keep the mask stroke from bleeding over.
You can, in the case of an arm for instance, mask only the hand (or whatever part you can easily mask) and then go to Mask > Grow Mask (I’d recommend Assigning a shortcut key to it, because SHIFT+R to repeat the last operation doesn’t work in Sculpt Mode!).
This works in 2.83 +, but I don’t know exactly when this was first introduced.
