Thanks, good idea with regards the lock. I did consider all sorts of options for the lid but it had to be quick as first I couldn't gain access into the tank (had tree frogs in) then the catch sprung open and wouldn't re-close! So as I didn't want to have free range frogs - something my three cats would have enjoyed, I had to move the frogs - quick! I had the mesh and it was relatively simple to remove the tub like seal from the inside of the lid. Pull the old mesh out, push the new mesh into place and replace the tubing seal - it just pushed back holding everything in place, as it is really tight I didn't bother with glue. Wish I hadn't ordered the new lids now!