Looking out from my first floor window a few weeks ago, I noticed the chair by the fence.

It was of the cheap green plastic variety and belonged on the balcony of the ground floor flat opposite. I just assumed that someone had moved it to get what little wintry sunshine was available in those dark days.

I live in a small complex of apartments protected by automated gates so I've always felt very secure. To one side of the block is a fence, behind which is an alley way and then the fence of the adjacent property. But, whilst I thought nothing more of it at the time, the chair changed everything.

Some days later, I saw another neighbour who told me of a concerning incident the previous weekend. She had noticed a stranger walking across the lawn between the flats and then he disappeared. Her son, who lives in the block opposite reported that he could see the intruder in the alley way between the two fences and then he clambered over the insecure gate and legged it.

When my neighbour had investigated further, she had found the chair pressed against the fence and an old case on other side. Someone had clearly been casing our joint and enabling himself a quick getaway. Obviously we moved the chair and the case, but it still left my ground floor neighbour feeling very vulnerable.

And then I remembered one of the first things that Martin Foster, the owner of Spy Alarms, had told me about home security. If you have an exposed fence, run some trellis along it. The trellis is insecure it makes it harder for someone to get a purchase if they try to scale the fence. And, if you grow something particularly sharp and spiky along it, that really does act as a deterrent, rather like a natural barbed wire.