Sadly, horse thefts do happen, but there are things you can do to prevent this
Keep your passport safe. It is illegal to sell, the slaughter of export a horse, without a valid passport. Your passport will also contain details of markings
Ensure that your horse is microchipped and Freezemarked
Take photographs of your horse, making sure you take some at different times of the year.
Make sure gates are secure. Put another chain and padlock at the hinges, to help stop the hinges being lifted
Good quality CCTV, alarm and security cameras if housed in a stable