I have been wearing a scabard that velcro straps onto the calf of my right leg. One strap is above the knee, the other is near my ankle. It is very handy but it doesnt always stay where I want it. It slips down towards my ankle unless tighten the straps to the point where it is very uncomfortable. Even then, after a few minutes it slips down again. How do I keep this in the right place?