I used to manage a few food trucks at a big outdoors bar and seagulls would steal people’s food constantly. We had a device attached to the trucks that would make a high pitched chirping sound to repel them labeled “sky rat repellent”
I also patented a technique in catching seagulls when I was a child. Lay a towel over you and sprinkle some food on top. Once they land swoop the towel over them. Apparently it caught on and kids were doing it everywhere and it became problematic because the birds were getting hurt.