We put in a 24 round above ground pool... our yard is graded and they had to dig 31/2 feet into hillside to level... now we have this ditch sort of likearound 3/4 of pool... what the heck do I do to hold back all the earth from sliding into ditch and the walls of the pool..?

There are a couple of things you could look at doing. Retaining walls can be made of different materials. You can use retaining blocks, which have the lip on the back to secure it against the blocks below. This may be the least disturbing to the remaining area. Another option would be to do something like rail road ties. If you do this you would need to dig into the remaining hillside to allow long lags/supports to be put in, to help with the pressure. These lags/supports would be of the same material and reburied, at different levels, behind the wall to help disperse the pressure. Which ever you decide to do, get some guidance from your local DIY store. They can give you the little tips of how to do this that I don't know that I could explain through here. I could recommend a store if you like, but it is up to you.