I've bedded the log roll in a concrete (mix 1 part concrete to 3 parts
ballast). This seems to have done the trick and it's very firm as it starts
to go off. The trouble with just bedding it into the earth (as I did in the
front garden) is that the pressure of the raised earth on one side can push
it outwards. I'm hoping the concrete will prevent this happening.

Cheers,

Ian