We have read an article in Your Cat magazine recently that gives a few suggestions to make your garden more secure.
Plant a country- style hedge
Even city dwellers can bring a breath of country air to their gardens by planting a selection of classic hedgerow plants like Hawthorn, holly, beach and dog rose. Once they have thickened up they will provide a safe haven for wildlife and a dense barrier.
Add mesh to your fence top
A sloping wire or plastic mesh barrier fixed to brackets on the fence posts will go a long way to secure your garden as cats don't like stepping out on a surface that wobbles. There are other systems on the market that could do the same job and companies to install them if you're not happy doing D I Y.
Plant a thorny hedge
Fire thorn or pyracantha is like living barbed wire and quite capable of deterring intruders, whether they be the local tomcat or a cat burglar. Plant a mixture of Berry colours for a feast of fruit that birds will also be able to nest safely in.
Erect a cat run
For total security an enclosed cat ran is the only solution. It can be accessed from inside the house via a dedicated cat flap. Make sure there are plenty of shelves inside for perching and elements to provide shade too.