Live Rock Aquascaping

[fishfogg]

Just how solid must i have my live rock stacked in my tank, some pieces are stacked farily losely because of wanting to create ledging's, no amount of water pressure would topple thing's over. As well i have tested each piece, by applying hand pressure on them they will stay put but if i were to push hard enough i could topple thing's over. Is this good enough or pardon the exspression does every thing need to be rock solid. First salt water tank so i have no past dealing's with live rock.
Thank's
Fishfogg