A lot is going to depend on the exact rules of the HOA, and what you
think you can get away with, as well as the dimensions of your
house, the type of roofing, etc.
My back yard is about the same width (but barely 20 feet deep, and
filled with plants). I got a telescoping mast that attaches to the center
of the back fence to make it easy to run it up and down. (Technically,
if it were mounted on the other side of the fence, it would not be
covered by the HOA!) I can string up full-sized dipoles for 40m and
a half size (coil loaded) dipole for 80m that is about the same size as
a 40m dipole. I could also use a full-size 80m dipole with the ends
running along the side fences (the bent shape may require a bit more
wire). For 160m, you could run a dipole to the corners of the fence,
insert loading coils, then run the ends along the side fences. You'll
probably need a shunt coil at the feedpoint, especially on 160m, as
the impedance likely will be low.
Using a dipole, even if it isn't very high, probably works better for
NVIS contacts in the local area - at least out to a couple hundred
miles, where a vertical tends to have a null in the pattern (although
using an "inverted L" may fill in the null somewhat). On 160m, you
will have to see whether NVIS or ground wave (which requires vertical
polarization) works better to the stations you want to work.
I do have a dipole on the roof for 40m, and am planning to extend it
to a "bow tie loop" to cover down to 80m - that might cover 160m when
fed with balanced line to a tuner. The antenna wire is #26 stranded,
with brown/green/black striped insulation, tied off with black micro cord
on the ends, making it virtually invisible above the roofline (except when
we get frost or ice on it, or the sun glints on it just right). I used to just
lay my wire antennas on the roof and tuck them under the corners of
the shingles, but asphalt shingles are much more lossy than the old
wooden ones. My current plan is to add extensions to my roof vents
(and add dummy ones where needed) to hold the wires up above the
roof somewhat.
Otherwise, I've also used a loop around the house, stapled to the back
side of the fascia boards under the eaves. You can put it up when you are
up on a ladder stringing Christmas lights and bring the feedline in through
the attic - it will be invisible to anyone who isn't looking right up under
the eaves. You can then feed it with a tuner, or make it a dipole and
add loading coils if needed.
None of these are necessarily ideal, but they have all worked at various times.