That sounds like vandalism, trespassing, and is clearly a violation of private property rights.
Committing crimes in order to get someone to cleanup their yard seems excessive. Jeez...
I said as a last resort... sheesh. I recommended just going over and addressing the situation.
It is like the lady that walked her dog and it crapped in my yard at least 3 times a week. I walked out and told her she was a rude pig for letting her dog crap in other peoples yards and not picking it up. She went off on me. Said she was going to tell her husband on me and he would come over and kick my ass. Next day when she came around she had the baggy. Now I just wave at her when I see her. No HOA needed.