If there are no objects interacting with the mud, make it using textures, interactive mud will take some doing, and could be rather complex to deal with when rendering. Especially if you are only rendering on one machine.
Complex Technology Development
I ended up going with two seperate solutions, for the place where i need extra detail I am using cloth (thanks to 3d kiwi) and where i am further away I have a displacment map and animated the bump.
Now i am compositing them in shake with the rest of the scene…seems to work.