WADR to both you and Wick, I think you overstate your case.
When I wear a neck sheath and small knife, I am also wearing a wool undershirt that is close fitting, and buttons up. I also have on an outer shirt with collar, and that keeps most any thing from grabbing at any necklace, string, thong, chain, etc. I might have around my neck. I don't start hanging upside down or even bending over low to do work without first removing thing that won't remain " put " when I am upside down. That includes my belt knife, axe, powder horn, possibles bag, hunting bag, glasses, pocket change, and knife, keys, and anything I have around my neck. I will remove my hat, too, and sometimes an overcoat, all of which will restrict my vision, or my arms in one way or another.
I have run with my patch knife in its sheath under my shirt with no trouble keeping it in place. You do have to think about all this, and not use one of those silly sheaths that only cover the blade of the knife. Mine covers about 7/8 of the length of the knife, including the handle. My sheath is tough enough to keep the blade from piercing it, unless a fall is hard enough to pierce my body with the blade, and sheath altogether. With that kind of impact, the least of my worries is being cut by my patch knife.