Rich_w, Sheet metal I thought would be easier to cut through, was thinking along the lines of something thicker, and aslong as their positioned as close to the centre of the wheel their wont be any way of it being prized off, although I do see your point about covering it all, might use thicker bars at the end like in the picture and cover the rest in sheet metal so it's not accesible!

Does anyone have a problem with the bar at the top feeling a bit flimsy, like it wouldnt takemuch to pull it off?