One point I would like to clear up that @Werner Geiger might be confused about is that Graphics does no computation - ever. It has no evaluation rules. Plot and other functions that produce a Graphics as part of their computation, but the resulting graphics object is inert.

Check out this. Maybe useful?

Manipulate[
    redcircle = Circle[center, radius];
    Graphics[{
        {Blue, Circle[]},
        {Red, redcircle},
        {Opacity@0.5, Rectangle[]}
    }],
    {center, Locator},
    {{radius, 0.5}, 0.1, 0.9, 0.1},
    {redcircle, None}
 ]

I am not shure, Henrik, if I understand you or you understood me. Where is that static Background in your example?

I added a randomly rotated LightBlue rectangle as such. Of course it is recalculated with each step, i.e. move of the locator:

grgr = GraphicsGroup[{Red, Disk[], Blue, Rectangle[{.5, .5}], Green, 
   Sphere[{.5, .3}, 1.4]}]; Manipulate[
 Graphics[{LightBlue, 
   GeometricTransformation[Rectangle[{-3, -3}, {3, 3}], 
    RotationTransform[RandomReal[{0, Pi/2}]]],
   Translate[grgr, {xy}]}, PlotRange -> {{-4, 4}, {-4, 4}}, 
  Axes -> True], {{xy, {1, 1}}, Locator}]

This actually works! At first I was surprised, because I thought the Show would be recalculated as a whole.

But now I understand it: xy is Dynamic, so only grgr is recalculated, background is not, because it does not depend on xy. Pretty simple and pretty stupid of me not to figure it out myself.

Thanks a lot!

Liebe Grüße and Glück auf!, Werner