Really shouldn't have to 'modify' or 'simply add to a design' to make a product do its job either it does or doesn't and in this case it's a definite does not! Our toddler has managed to fit all kinds of things in between the gap. There was an older style toilet lock that swung down, I can't find it anymore, so we went with this one. Well so far he's managed to fit a remote, crayons, pretty much anything within an inch and then some wiggle room in there. Im less concerned about his safety at this stage in the game and more our plumbing.
Please don't waste your money or think the reviews about modifying it will help, toddlers are so smart and will bypass your add ons, just buy a better toilet lock.