From my limited experience, it's difficult to use a Defender to tension the fence.
You can get the initial tension on, but then lose it again when you take your foot off the accelerator and put it onto the brake. You then lose a load more when you switch to the handbrake because it works on the transmission, not the wheels.
If you have a friend who can help you to heel-toe the pedals as it were, that may help. However, the last time I did it, I threaded an iron bar through the rylock, then used a come-along hand winch attached to the parked landy (wheels chocked) to apply tension between it and the iron bar. Just something to think about, though others may have better methods!
I also bought a copy of the BTCV Fencing Handbook by Elizabeth Agate, which was well worth the money.