I would be really interested to hear any constructive comments, and how
other people had tried to reduce noise in their gardens

Not tried it myself, but there are several manufacturers of "acoustic
fencing" if you throw that term into google...

This one also gives an idea about the level of reduction you might get
from their stuff...

http://www.jacksons-fencing.co.uk/pa...prod_det.aspx?
tpc=AS&fmc=BV&fnc=AX

or

http://preview.tinyurl.com/yvtgud