First, check to make sure you are locking the lid into place. The lid turns clockwise and stops; to lock it in place you must push down on it and turn once more clockwise to make it go into the locked position. If you have been doing this and the lid still comes off then most likely some or all of the hold down wedges on the side of the canister that lock the lid in place have come off. We have made a change on the Paramount leaf canisters in this area and the new part is called a canister ring stop. This is available to retro fit into your older style canister Part number 005-670-6192-02.