Stop it sliding
A bar or dowel in the track, or a hinged security bar, stops the door from opening even if the latch is beaten.
Stop it lifting
Many sliders can be lifted off the track. Anti-lift blocks or screws in the top track stop that.
Fix the latch
A worn latch or a door that has dropped on its rollers often does not catch at all. New rollers and an adjusted latch fix both.
Add a keyed lock
A keyed patio lock or a foot lock adds a second point that cannot be reached through the glass.