Back-up knife & "the wave"
Not to plug a particular brand name, I will use what ever works, but Emerson Knives have a technology called the "wave." I carry an Emerson Karambit on my weak side as a back up. It is a stout folder that has a large finger loop to draw the knife. When drawn, the "wave" catches on your pocket and automatically opens the folder.
It is a slick system and Emerson offers several different varieties of folder and fixed blade knives.