If your property has been a target of burglaries several times before due to easy access to the back garden, and the usual deterrent’s are not enough to stop the burglars coming back. You may want to consider installing a trap zone in your garden, where you can release non-toxic smoke to confuse the intruder, and then activate some sort of security cage that comes up from the ground and trap them inside once they have stepped on a series of pressures pads that activate it (they will detect a certain amount of pressure before they are released, so a small animals won’t trigger the security system).
Ideally they won’t see the cage coming up and by the time the smoke clears they will realise they are trapped and will try to escape, though the cage will be high enough that they won’t be able to climb on and escape from. Using the concept of a cage coming up from the ground as opposed to closing doors and falling cages means you are not going too be sued from injuries that may occur as a result of those other systems.
This way, if a burglar knows they are likely to get caught, they won’t see your property as an easy target any more and will be deterred from trying again.
These systems are fairly easy to install: A small small thin channel can be dug along all sides of your patio area, and a hydraulics system sunk in at the bottom, where a collapsible security cage is fixed too; the security cage is is similar to a folding cross shaped elevator door and should only be about 2ft in depth when retracted into the ground and about 8ft height when extended up from the ground.
This system may be costly and might not be available within the UK (Featured in a DIY show in the US), but if you look around you may find them online.