The Cachekeepers: This was a tube stuck in a brick, underneath a stile.
No matter what we tried, the lid always went missing. We painted that lid all sorts of colours, to stop it from leaping into the grass and disappearing. In the end, I'm afraid that we stopped replacing it as often and hoped that the waterproof log would remain usable without it.
I really wish we could have found a supply of lids, without the tubes. We have a box full of useless, lidless tubes. I think most C.O.s who use these screw-top tubes do.