Not sure if anyone suggested this yet but I am a thinker. I know there is damage to your property now that needs to be accounted for. On the other hand if it keeps happening here is what you do. every arrow that ends up in your yard you snap in half and throw away like you would a fallen tree branch. eventually the kid shoots them all in your space and the dad gets sick of buying him more arrows. once they hit your property they are yours. That's what i would do.