Guard dogs were once used widely by people wanting to keep their properties safe. Some people still make use of them, especially in commercial properties and properties that are in more rural locations. There are definitely more modern ways of protecting your property, though.
Remember that dogs can be greedy and will be led by their stomachs. If a burglar or intruder really wants to gain unlawful access to your property, they may be able to tempt the dog away with treats. Even the most well-trained dog can be persuadable when hungry!
If you do choose to have a guard dog, it is definitely a good idea to combine this security method with others as well. Invest in a good alarm system, put up gates and hire a security guard to monitor who enters the property. Make sure all locks work properly and have everything serviced regularly to check the security methods you have in place are still working effectively.