Ants and aphids

Hello all from Nova Scotia.  I'm hoping someone may have some info to help
me.  I have a huge ant problem in my yard.  In our back yard we have no
grass, a pond surrounded by pea gravel pathways and stone, along with
concrete pathways with bricks bordering perennial beds.  Our yard isn't
really very big, approx 30 x 30.  In recent years we've had huge numbers
of
ants (I think a lot of people have had) and I've always had aphids in my
plum tree.  This year however I've noticed aphids on my 3 clematises and
on
a shrub in the front yard.  I've never had before or heard of aphids on
clematises.  I'm wondering if the huge number of ants have something to do
with my increasing aphid population.  My husband says ants "farm" aphids,
I
think he means they sort of herd them 'cause the ants like the sticky
stuff
the aphids excrete after sucking the good out of a plant.  Anyone know
anything about this?  I use soapy water to combat aphids which does kill
them, but often the damage is done.  I know of nothing that will kill
large
amounts of ants.  I know of the store bought and even home remedies but
they
are difficult to apply to an entire yard.

Any suggestions?