In reply to planetmarshall:
If you're feeling like splashing some cash, I got one of these (they post to the UK once you email directly instead of using the online shop).
http://smartrock.de/home.html
I had a homemade rigup, but it wasn't particularly clever and was awkward as I needed to be able to take it up and down regularly.
The flashier version can even be calibrated to an app on your phone to measure and track progress.