I play Middle Eastern and similar strings (ud, cumbus, cobza, Puerto Rican cuatro) and use the traditional kind of plectrum for those, a few inches long and cut out of a plastic soft drink bottle (or the plastic strapping used for packets of building materials, which I find work better for the louder instruments). If the instrument's sitting around out of its case I thread them through the strings near the nut.

I use to have a cat who thought they were cat toys. Every so often I'd hear a distinctive loud BOING and a scampering sound as Zeke would drag the plectrum out of the cumbus with his teeth and run off with it. A few months later I'd move a piece of furniture and find the very dead plectrum underneath it, curled up and dented with little toothmarks.