In this thrilling installment I've included a couple of photos of my trial of a way of installing a straining post strut, based on a method described in the Forestry Commission online booklet "Technical Guide - Forest Fencing" (60 pages, not fully studied yet). In this method the strut is not embedded in the ground. I placed the end of the strut on a flat stone, secured with a nail through the "thrust plate" stake. The stake is tensioned towards the straining post using strands of wire, but there seems to be an error in Fig. 5a on page 7 of the document - the wire should be on each side of the strut.
I thought an advantage of this method was that the strut may be less liable to rot, and the wire could help prevent the strut slipping laterally. I'm not sure about using a nail to fix the strut to the stake, but I used one having pre-drilled the stake to reduce any tendency for it to split. A possible disadvantage to consider is that animals may get caught in the straining wire, but a section of stock wire could be fixed to the normally unwired side. As usual, I failed to line up the struts on the straining post, but perhaps that may weaken it less.
Note: This was part of a relatively short fence (10m + 30m) which didn't require a very high tension, hence the small diameter straining post and short struts).
Update Feb 2019
I've added a photo of the completed fence section, but I don't know if it's still standing! In this situation, with the wire on the inside of an angle less than 180 degrees, the wire is routed around the back of the strainer, so that the post holds the wire tension not the staples. (click for larger image)