On Sat, 23 Dec 2017 16:37:24 +0000 (GMT)
charles wrote:

Our present small fence (to stop people driving into the ditch in
front of the property) is made with pressure treated uprights.
Unfortunately, they are not always visible (under trees) to delivery
drivers, who have managed to hit them, or at least the horizontal
timbers they support. This has ressulted in the main uprights
breaking - they neeed to be replaced. I wanted to make the uprights a
bit more visible - I can't really paint pressure teated timber.

You might do better just to attach some conspicuity aid such as the
standard yellow and black reflective film on an aluminium base, with
which the drivers will be well acquainted.
Or as I already wrote - galvanised steel box section. :-)