My cats always liked to sit on the window ledges (old house, wide ledges) and would invariably break off slats or parts of slats from my mini-blinds. The mini-blinds are the old metal ones, not the newer plastic (vinyl?) ones. I also resisted using them (the blinds, not the cats) but saved them for a friend who used them for labels. One day I was out of my 'regular' labels so I grabbed a broken slat. I trimmed it and made sure that the bottom would be pointed to make it easier to use in a potted (so to speak) plant. I've been using the permanent markers for writing and that seems to be holding up.
Just hope there's nothing too toxic in that ink. Oops. Hadn't thought of that.