Hello everyone and thank you for responding. Regarding the height of
the fence. The elevation difference between the neighbors yard and my
yard is about 3 feet (I'm below).The fence is on top of a retaining
wall. I was thinking that a difference of 9 feet would make somewhat
noticable difference in noise level. The pool filter sits right next to
the fence (about a foot), so any sound barrier on the fence would
greatly reduce that noise. Their pool is fairly close to the fence
also.

The parties are kids parties, and being a kid at one time, I remember
always screaming when having a pool party so I'm not going to complain
to the neighbors about that. Kids will be kids, at least it's seasonal.

So I'm still trying to figure out something I can perhaps "fill" in
between the pickets that can withstand the weather.