Posted: 04/06/2013 at 16:44
When we moved here there was a huge Leylandii hedge at the front - over 15ft high and 3ft across. It was a pain, and took three days to cut it safely - and then there were all the clippings to get dispose of . . . until the next time.
We decided to get rid of it, but, because it was sited next to a wall which would have been compromised by taking out the stumps, we had the trees cut down to ground level We then did exactly what you are thinking of - namely create a raised bed to cover the stumps. Providing the subsequent planting is of shallow-rooted plants, and provided you add lots of organic matter each year, it is a successful way of dealing with the problem.
It will take a long time for the stumps to rot down, of course, but they will eventually. We have a lovely shrub border there now - a combination of hebes and wigeliia infront of which are smaller shrubs like cistus purpurea and spirea, as well as perennials. Overall it has worked well.