Cotton balls are the answer. They're not heavy, and they are biodegradable. What you do is, you pelt the malefactor with cotton balls until he, she or it gets annoyed and leaves. Some kinks to be worked out.
You could also hold a cotton ball near their ear and roll it between your fingres. Some people can't stand the squeaky sound it makes.
Just thinking about that made me shudder.
I cannot even touch cotton wool, let alone that squeaky noise, or the sound of it tearing. That is true evil.