looking for advice

Hi Joe and Angus

I have had a late thought (this happens to me a lot) have you heard of Hugelkultur?  Permaculture method where they make big heaps based on a pile of logs/branches the idea being the wood breaks down slowly proving nutrients.  I just thought this might help you as it would fill the bed up, if you can get hold of some branches, and as they rot and sink down you can add more compost or whatever as you get hold of it.