I have never done parkour. But for the gym, crossfit, PT test, trail running and jogging I just carry my EDC (Hinderer XM18 3.5) clipped IWB of my gym shorts in the appendix position. I don't see why it wouldn't work with any reputable folder with decent clip tension. I have also used a Spartan enyo neck knife but I can imagine a neck knife would be cumbersome when flipping though.