I was old school. I bought a flat piece of slate, then several rubber bands. Attached spinach leaves to the slate with the rubber bands, set it in the water. A few days later I removed the slate with a handful of fibrous veins left over. Slate was pretty heavy/stable so it didn't move around the tank even when my pleco was 10-12". Anything you can slice into long strips (e.g., cucumber) or that comes in large leaves (spinach, kale) works.