For what it's worth
a) The declination (+12-59) at Traralgon is about 1.5 deg different from Melbourne (+11-33) [
http://www.magnetic-declination.com/]
b) The declination for Rockingham is close to -2 degrees
c) Solar noon is only correct 4 times a year [
http://www.ips.gov.au/Category/Educa...tionOfTime.pdf ] (up to 16 minutes or 4 degrees : mid-Feb and late Oct)
d) the "star trail" idea is not bad!
My suggestion: Look at your property title and it will show the true bearings of your boundaries. Get some string and use simple trig to lay out a reference line in your garden.
OR - visually locate Achernar and Beta-Centauri and split the difference.