We have not done the film yet. It is procrastenating on the to do list....Not to be nasty but you are wasting your time with the film. I they want in, film is not going to do anything except make it nice and quiet when breaking the glass. I always believe the true deterrent is to increase the visible difficulty in gaining access to your home as a deciding factor. However, if you have large windows with no barriers, installing a barrier against the sliding door is going to be just as pointless ( as per your point ), they will go through the windows instead.
I'd just increase the lock on the sliding door somehow, possibly even some form of deadbolt so they would have to smash to gain entry.
We have 2 locks and obviously the normal latch. The one lock is by the latch, like many would have. The other lock it sortof like a deadbolt. It is well anchored into the wall with a large pin/lock thing that goes into the door.
It can be lock by pushing or slaming it in once the door is closed. You need a key to open, but not to lock it