[Wavytone]

Lewis, DGPS is one way. Without DGPS there are other ways:

(1) From your longitude, calculate when local solar noon occurs, to 1 second. Instead of using a shadow, set up a small lens with a long focal length to cast an image of the sun on card as it passes through local solar noon. Assuming the lens is fixed, project the image if the sun onto a filing card that has a circle drawn on it the size of the sun, and a vertical line (north-south) through the centre.

Manually move the card to follow the suns image keeping its disk centred on the circle. At local solar noon, stop moving the card. The central line gives you a very accurate measurement of where the meridian is.

Reading glasses of 0.5 dioptre from a chemist will do nicely, put a diaphragm in front to stop the lens down to a 1 cm diameter. For a focal length of 2 metres the image will be about 20mm across. With care you can make the measurement with an accuracy about 1 mm - which corresponds to about 1-2 minutes of arc since the sun is about 30 minutes across - far, far better than using shadows.

(2) If you can obtain 1:50,000 or 20,000 topographic map of your locality, or even better, the surveyors "deposited plan" or DP of your block of land - plot your telescope position on the map and find a distant landmark on the map visible from your telescope position, and put a nail (1) where this intersects your fence. Determine the azimuth accurately using the map coordinates. Using trigonometry, calculate exactly where true north or south intersects your fence.

Google maps or the stuff you get on smartphone apps are not sufficient for this.

Using your finder scope to get a bearing on the distant target, use a tape measure to measure the offset from nail (1) along the fence and put a nail (2) there. If you are using a fork mount, this should give you true north/south fairly accurately. If using an equatorial, you will need to make a correction for the lateral displacement of your finder from the RA axis.

If you have the DP for your block of land (this is usually included in the contract when it was purchased) take a close look at this. There are often measurements and precise bearings shown from boundary pegs to surveyors marks nearby, these can be crows-feet or drill-holes in the kerb or to trig stations if visible from your block. The worst case is when they reference a survey pipe buried under a pavement in which case you are out of luck.

(3) Another method if you don't have an accurate map, but (a) you do have a GPS (smartphones or iPads will do) and (b) you can see a distant landmark. Using GPS measure the lat and long of your telescope. Then measure the position of the landmark (go there). Note that the smartphones and commercial GPS accuracy will be about 3-5 metres at best, so to get accuracy around 1 minute of arc the landmark must at least 2km away. Using trigonometry, calculate the bearing from your mount to the landmark. Then work out where north/south is with respect to the land mark as measured along a fence, and proceed to use nails in the fence as in method 2 above.