How to cut marble mosaic deco tile?

I have to install a stip of decorative border tile all around the tub area near the ceiling... it's 24" long, 2 1/2" tall and made of little hand-cut marble bits set in a net backing to look like a beach scene or something. Anyway, I will need to cut it to length at some point. I have a wet saw, but how to I cut it and avoid throwing needed bits of marble all over the garage walls? I mean, won't they just fly off the backing instead of being cut? What should I do? Should I tape it up, hold it upside down, and cut slowly? Or, should I carefully cut the backing and make it the approximate size I need, then make up the different with grout? How do you correctly cut this stuff? It's expensive too, so no room for errors!! Thanks!