We built two 4x4x4 bins last summer and have been adding everything uncooked that the school kitchens give us, bread, egg shells, even things with mayonase like coleslaw, along with all the lettuce, cabbage leaves etc. In the garden we chuck on everything we pull out of the ground, and I put the cardboard in. It has all rotted down marvelously, and much has gone onto our veggy patch. I haven't seen any rats, but I have seen some of the onion skins taken away and left by the fence!! Recently, when I turned the whole lot out, I was supprised to find lots of strips of plastic amongst the semi-rotted compost ... these turned out to be the sellotape from the cardboxes I had put in!!! Also, I found a box that was plastic coated that had obviously not rotted away. So, I will of course be far more vigilant from now on as to what is attached to the cardboard I put in the heap!!