Lighting is still recognised as the most effective intruder deterrent, and courtesy and safety lighting and sockets can double up for security.
Most customers will opt for automatic wall-mounted lighting. Thankfully the days of prison-camp style halogens are long gone, and the new generation of stylish robust LED lighting will do a perfectly good job for you. If the primary purpose is security, you may want to install the lights higher upon the wall where they cannot be tampered with, so make sure they are going to last the course (built to resist corrosion so they won’t just go rusty after a season) and easy to install and setup when perched up a ladder! Look for easily-wired back plates that you just click the main unit onto.
Decorative lighting at the end of the garden can also play its part in making sure intruders have nowhere to hide. If its powered from outdoors sockets, make sure that they have integral time controllers or RCDs and, if security is a key consideration, that the covers have locking bosses like Timeguard’s Weatherproof Extreme range so the intruders cannot just flick them off.