Locking a DIV

Locking a DIV

Sup ppl,
Just one question about layers and stuff it might be easy to solve this one with JQuery. Thing is as follows...
I'm working on this website layout which has loads of DiVs in order to place every single part of the page properly around the layout!... i got a dinamically size increasing tree on a layer wich grows whenever certain event is triggered but then it grows over the footer layer which is located on the bottom of the layout. What im trying to achieve here is to remain the footer layer in the very bottom , no matter what happens or who grows... it must be down there... How could i tell a layer whether through css or Jquery not to walk over (above) another layer???
I tried using float... nothing.... then i tried with overflow = "scroll".. nothing...
Any hint?

Best regards.
Jmc.