You can rent lockers at all of the parks. They are at the front of the parks as follows: Magic Kingdom; under the train station. Epcot, to the right as you enter just past the photo shop OR at International Gateway just to the left as you enter. Disney Studios; Oscars Garage - to the far right as you enter, but you pay at the Large Kiosk in the center of that area. Animal Kingdom I am unfamiliar with.
They are $7 for the day with $2 refunded when you return the key. If you are park hopping, hold onto your receipt and just show it at the next park for your next locker.
Hope this helps!
Have a Magical trip!
