Oh guys, I'm about to change your world. I learned this trick from Thoughtworks (and those guys know post-its!).
You need to peel your post-it notes off from one side to the other instead of tearing straight up. Then once you stick it on to something it's holding power is magnified!
There's even a video of how to do it https://www.youtube.com/watch?v=Zj8EFqVoqYE
May your post-it notes be forever sticky.