Toad n the vole

Slowies never go under this toad sack but they do go under plastic sacks I have about. They also go under upturned plastic tubs. I force rhubarb in spring under large tubs stuffed with straw (can't afford the lovely terracotta ones!)and I got quite a start one day as a slow worm had climbed right up through the straw and rhubard shoots to the top. I figure they don't use this flat-on-the-ground sack as it is out in the open with no vegetation to slink through to get to it. Perhaps feel too vulnerable.