I would be happy to lift you up to make sure it holds fast.
If your PFD is tight then it isn't needed. If you keep your pfd loose then maybe you need a wedgie strap. The strap at the bottom that goes under your rib cage is supposed to keep it on under any circumstance.
I have been told by many rangers at various put in's that the strap is not a substitute for an inadequate pfd, such as a water ski vest.
May the wind be always at your back,
May the sun shine warm upon your face.