thanks for the all the replies, for the retaining wall i plan to use concrete fence base panels (probably two, one on top of each other) with wooden fence panels on top.

the "pool soil" is a mixture of clay and sand really. when it dries its grey. i have been trying to level the soil as much as i can and removing rocks etc using rakes and spades....my arms are killing me now much to the amusement of my girlfriend

i think its a pretty good idea regarding using this soil as a filler, then nice fertile top soil on top. how deep should i be aiming for with topsoil?

would i put the manure on top/ mix with the "pool soil" or when i get the top soil?

the soil that was originally in the garden (under the concrete) had quite alot of clay in it.