My lock is under the headrest also in my car. I would make the top as tight as i could, hook it first and then hook the bottom ties on the locks in the seats. They also make something called a "T" hook that can help lock it tighter. You can also run the seat belt through the back of the seat to lock it down tighter (make sure to "lock" the belt when doing this). That is if your's isn't a booster seat. Most newer cars/trucks/suvs come with the locks in between the seats, you will have to reach your hand in there to find them, they are usually shaped like a U. Hope this helps.