you should be able to move the dock to all four edges and it stay there.
Psst, Phiily; it is the start menu from the start menu docklet that is moving not the dock.
It may be a version 1.9/Windows7 thing, the Beta of version 2.0 runnings much better on XP, Vista and 7 than version 1.9 did.
Since it is in beta there is no free version, you would have to purchase, the bundle includes both the 1.9 version and 2.0 Beta.
https://www.stardock.com/products/objectdock/