I bought a leather “obi” (Japanese sash) belt at a car-boot sale, originally from Topshop, and decided to modify it by cutting a scalloped edge.
I got the idea to make a scalloped edge because the belt is a thin, flat piece of leather with no stitching, and I know that leather doesn't fray or need to be edged. It will work with any leather belt which is thin enough to cut with scissors. Note that in addition to cutting the scalloped shape I also cut the belt a bit narrower..
Draw a series of semi-circles touching at their widest point, on the reverse of the belt. Do this by tracing the shape of a round object like a plastic lid or a large coin. I used a spice lid, and made sure that each semi-circle just skimmed where the edge of the belt would be so that they were all in line.