I've got some line laid on breeze blocks which have a concrete 'footing' (yes, almost certainly over-engineered!), with other sections running on decking boards covered with roofing felt. The garden is heavy clay (we had to go down 3 metres for our extension footings

) and seems to shift a lot in places -I'm currently planning a re-lay on a section that looks to have dropped 25mm or so over four years). I have to say that whilst I like the
idea of laying a blockwork base, I'm happier with the timber sections; the latter are also easier to level.