Regarding your query on guarding, this breed is considered as a good guarding dog.http://en.wikipedia.org/wi ki/Cane_Corso
There's is a misconception among us on a watch dog and a guard dog. People use them as one and the other but they are actually different. A watch dog can alert his master about any potential threat to the owner or his property. ALL DOGS HAVE THIS ABILITY. You may have seen a pet dog barking on the gate of the house. This a doing a duty of a watch dog. The watch dog will alarm his owner about any suspicious activity in his surroundings. The watch dog may be able to scare the intruder off but he may not able to CONFRONT him face to face.
This ability of confronting the intruder is the ability of guarding. A guard dog can not only scare an intruder off but can also ( if required ) potentially attack him. Breeds like German Shepherd, Rotweiller, DobermannPinscher, etc are renowned all over the world fo their great guarding ability. The guard training is called schutzhund training. Watch is video on schutzhund training which will help you understand even better-http://www.youtube.com/ watch?v=Tfm3rQspCEY
If you have any other enquiry, don't hesitate to ask.