My water butts are re-cycled plastic chemical drums and are impossible to keep covered, I've tried many different methods, but the slightest breeze dislodges everything I try. Last year I had to rescue loads of bumble-bees from them, and I assume that when I wasn't around plenty were not so fortunate. Would an old broom handle or bamboo cane in the water allow them to climb out? Or can anyone come up with a fool-proof method for keeping some kind of cover on them.