First off, put tools away as soon as they are finished with, and keep gates and sheds locked.
When it comes to securing boundaries, there is something of a conflict. The screening that provides privacy can also be the cover that the intruder needs to effect an entry. A compromise is to make it as difficult as possible to get into the garden, but have boundaries and outbuildings visible from the house. There is no more effective barrier, for people just as for livestock, than a dense, thorny hedge. Hawthorn, berberis and pyracantha all do a sterling job, being viciously armed and ornamental to boot. If there is no room for a hedge, any fence or wall can be made harder to scale by topping it with two or three feet of wooden trellis.
Paint, indelible pen or engraving can all be used to mark equipment with your name and postcode. This makes items much harder to sell on and thus less attractive to steal. If you really cannot bear to sully your shiny new mower, use a UV pen instead. At the other extreme, customising all your gear with a coat of bright pink paint will make it immediately recognisable.
Make sure sheds, gates and garages have sturdy locks or padlocks. Bulldog manufactures an excellent range that includes a sliding bolt with an integral locking mechanism. Internal hinges (and, if possible, locks) that are concealed when the door is closed are more tamper-proof than exterior- mounted fittings. Inside the shed you could increase security by using a wall anchor - in essence a chain which is threaded through equipment and then locked on to the wall. The Metro Stoplock wall anchor is a particularly robust example.
Outside, stone urns, large pots and statues that stay in one spot are best concreted or bolted into place to prevent them wandering off. New plants are easy prey, so try not to advertise their presence. For large, precious plants you may even want to put in a ground anchoring system, such as that available from Platipus.
Outdoor lighting makes life harder for the intruder and easier for the owner. Most DIY stores offer a wide range. For security purposes the most useful are those with a passive infra-red detector that switches on in response to heat or movement - a nasty shock for any intruder, though something of a nuisance if it's only a cat.
The next logical step up is alarms. Most are activated by detecting movement, or when contacts on doors and windows are broken. With the arrival of wire-free technology it is a simple job to extend a house system to include outbuildings. If you harbour a real desire to apprehend rather than simply deter, you may be interested in the Excalibur alarm from Databuss. This is silent at source but sends a signal to an alarm in the house. A quick phone call to the police, and the thief can be caught in the act.
The ultimate solution has to be a closed-circuit TV camera. Response now offers a kit that plays back through the TV set for less than pounds 150. I'm not sure whether watching a break-in from the comfort of the sitting room is my idea of fun, but I suppose the subsequent police chase in the garden could make for gripping viewing.
What of the allotment? I hate to be defeatist, but none of the above is going to be the slightest bit of help. All I can do is to take everything home at the end of the day, and have my next shed insured through the National Society of Allotment and Leisure Gardeners.
Databuss Electronics 01633 214455; Metro Products 01293 533663; Platipus Anchors 01737 762300; Bulldog 01952 728171; Response 01372 744330; National Society of Leisure and Allotment Gardeners 01536 266576
Tom Barber presents `The Garden Party' on Channel 4 at 8pm on FridaysReuse content