Well, since my hair is down to my knees, I sympathised at once.
Hairpins can be very bothersome.
I use mostly large flat bobby pins and large U-shaped french pins. This pulls the hair in the bun tightly together with the hair closer to your head. Also, if you arrange your hair loosely, you can expect to lose the pins all over the place. I can only speak for myself, having thick hair that weighs a ton, I have to braid and arrange it neatly and tightly or it will collapse. Those who have hair that will make lovely tube curls and stay that way are lucky.