I would talk to them in a non-agressive manner first........people are more receptive if you seem nice and not combative. My neighbors below me came up to talk to us about a few nights everyone was really drunk and peeing through my deck onto theirs and puking too........they asked so nicely like "I'm really sorry to bother u but could u please when u have friends over have them puke and piss over the balcony and not onto ours, i'm terribly sorry to have bothered u and i found it kind of funny but my mom came over to visit and walked out onto the porch and saw it all before us." I felt so bad about it now i don't even let friends out onto the porch unless they are smoking a cigarette or something

I guess what I'm trying to say through my rambling is just try to act friendly and courteous and most of the time people will be more willing to see eye to eye with u

EDIT: if talking to them nicely doesn't work, then yeah maybe the whole cinderblock idea would work