When you want to secure your sliding door there is more than just a lock for the Center of the door. For the top and bottom in most cases you can install patio bolts. They can also be keyed alike to most standard house keys. When secured the only way to open them is with a key from the inside of the door. Very hard to tamper with the screws holding them as these are covered by the bolt. Available in most colours like silver, brass, black or brown. They are a fantastic way to beef up a typically hard to secure door in your home. There are many different brands around but your best to stick with the ones that have severed many homes for a number of years like the Lockwood 680 patio bolt.