I ran into that problem with the ring on my folder. I started out with the largest Chain Disk that was available, but that was not enough. I then carefully studied how the pants get stained and realized that this consistently happens in the vicinity of the crank. I ended up cutting out 2 triangular pieces out of alu that I first glued and then riveted, I think with some L bracket, to the Chain Disk by the crank. I.e. when the crank is up, those pieces cover the sides of the crank so that the three form together the shape of a volcano with the crank being the core of the volcano. This arrangement works pretty well and I do not need any velcro straps.