A security bar that fits right in the track could do the trick.
How to keep sliding chicken door secure.
A good way of doing this is to insert a bar into the tracks of the door to impede movement and prevent them from being opened.
A lock pin like this one or this one links to amazon is a very simple and inexpensive way to secure your sliding door.
Remove any source of temptation like trash pet bowls and other food stores from your yard or stash them in bear resistant containers away from your coop.
If your coop s ventilation openings are covered in quarter inch hardware mesh that s great but how well is it attached to the coop.
If you attached the corners with flimsy nails you might need more.
Want to keep those doors from being forced off their tracks.
Good ventilation is essential in a chicken coop but make sure you have secure ventilation.
Slip in a security bar.
Lock doors and windows at night.
The height of the chicken coop door from the ground outside doesn t matter as long as chickens have a ramp to access doors that are 18 24 inches high.
Strive to build your chicken coop as solidly as you would your own house and install an electric fence or electric wire around your coop and run.
The latch locks on the door can easily be compromised so you want to make sure that the doors have a secondary level of security to deter burglars and offer up a good fight.