I've been struggling with a similar problem myself so I'm following
this thread closely.

Whilst I agree it could be a neighbour thing in my case It can't be.
I keep the conifers down to
a manageable height - 6' - and they act as a hedge separating 2
lawns. I
don't have any neighbours on one side & the on the other side his
trees & shrubs are
so tall & thick he couldn't see mine if he wanted to!!

I had to remove the complete hedge on one side of the path & now the
other side has
started.

Vera