Work out your "solar noon" from
https://www.esrl.noaa.gov/gmd/grad/solcalc/ (click a purple "balloon" and an orange one appears which you can move to your location).
Solar noon is the time the sun crosses the meridian as you know, so use a vertical stick in the ground as a gnomon and mark the shadow it casts at the time the website gives solar noon as. That is a perfect north/south line.
Hope that helps.
Stu