Raised flower bed alongside fence

I have had a new 2 metre high garden fence installed in my back garden and I want to build (I mean get someone to build ) a two foot high decorative wall about 2ft or so away from the fence which I can use as a raised flower bed. Should I protect the fence with some sort of plastic sheeting or membrane before we fill the bed with compost. I don't like the idea of putting the soil right up against the fence as I am sure it would rot over time. Hope this makes sense, any advice would be much appreciated.