Old English Mastiff

Question
QUESTION: Hi Nancy, I have a 14 month old Mastiff. He is very friendly with everybody inside and out of the house. He jumps up on the fence to get his weekly stroke from next doors gardener.He never guards his food,toys or bones. he likes to chew on his bone at your feet and sometimes gets you to hold it while he chews on it. last month as I was cleaning up his things he growled and started snarling at me in a very aggressive way. because I didn't move away he got up to bite me, so I had to leave the room because he is 11 stone of dog. never has done it again until this month he did the same thing when I went to take off his lead which I do twice a day. Yesterday he attacked the vet for know reason other than it was a hot day and he wanted to go home. Do you know what is happening here? any help would be great. Please note he goes to dog training twice a week and is the best dog in the class.everybody loves him.
ANSWER: Keeley,
What does your trainer say?  Mastiffs can be very aggressive when they reach maturity, unless you have been in a dominant role all along.  It sounds like he is challenging for the Alfa role and he is winning.  Go immediately to someone who knows mastiffs, and aggressive animals.  You need someone to direct you in this and watch how you are with the dog so YOU and the dog can be both encouraged and corrected.  In the meantime, go online or to a local army/navy store and buy pepper spray.  Always have it on you and the next time he even looks at you funny spray him in the face.  An 11 stone animal could ultimately kill you if he had a mind to.  There is one more thing to watch for with him.  Any funny happenings such as him looking around at something when nothing is there or other strange things.  A brain tumor can effect the personality of dogs.  I don't think this is the problem, because you are not the first person I have talked to with a mastiff with these problems.
Nancy

---------- FOLLOW-UP ----------

QUESTION: Thanks Nancy I think you're right, the two trainers I have think I'm a great dog trainer and it must be a tumor because he is so friendly and good in class, since the last text he has started barking at things like kids or a bag never done this before. But I still think he is challenging me. Thanks for your help.  

Answer
When I wrote you last night, it was after a 13 hour workday, and my brain was not functioning as well.  I believe something else may help you.  Dogs like mastiffs, rotties, shepherds, etc.  need to have a purpose or their energy level builds up and comes out in a bad way.  You need to "work" him more.  Think of something that will do double duty,  tired him/fulfill him and at the same time keep you as pack leader.  I would get a back pack for him and load it with water bottles (heavy) and walk him or even better you bike and let him run next to. for a couple of miles.  Of course work up to this, start slow, but remember dogs stamina is great.  Contact the breeder, as well, and see if they have suggestions.  They know the breed better than anyone.  Your two trainers, don't seem to know the breed well, and you need someone who does.  If you are pushing him to work, you are "pack leading" if he grows very tired all the better.  Keep your pepper spray, always for now.  you should get to a point where you don't need it.  I agree with you that he is challenging you.  
If it comes up again, (aggression)do the following all at the same time.  say "aaag" in a gowly low voice, throw something at the wall behind him that makes a noise, and walk off in front of him.  Make sure he is distracted by the noise before you walk in front of him. and when you walk off make it businesslike, try to avoid backing away.  make it like it is unimportant to you.  Now this is NOT what a pack leader would do, but this may keep you out of immediate danger.  a pack leader would over come him, but that should be done when he is very tired right now.  well good luck, and pick up a tape of Cesar Millan.  he is fabulous, he has 32 pitbulls living together with him as leader.  He is also more gifted than the rest of us
nancy