What to put under tray (1 Viewer)

I already have a bird feeder with a dome. The other side has water with a dome. There is no more room to hang anything only for a bowl at the bottom but the food gets wet when it rains so the birds don't eat it. I bought a non toxic pet tray for the birds where I fill up 2 bowls of bird seeds and put it on the tray so the wind cannot blow it. It works. But I need something to put under the tray that is non toxic and safe. I read online that even cardboard boxes are toxic... I thought about putting a rug but I don't know if it's considered safe for animals to eat from a rug since they might end up eating the rug by mistake. I just need something to put under the tray. The way it is right now the birds are crapping all over the cement. I don't want this... I also want to make it easier for me to clean. The wind blows the bird seeds that are on the cement which makes it harder for me to clean.