Q: I am the proud owner a beautiful 5-month old female brindle Mastiff. She has been with our family since she was 9 weeks old and has been a delight. Just recently she has been acting out towards our children. It's almost as if she thinks she's in higher rank of them or is testing the waters to see if she can be. My children are small--1, 3, and 5. They are always supervised and are not allowed to play with her unless we are in the room. The children love and respect her, and are not mean or rough with her. When we first brought her home, she was very timid and followed me everywhere. She was very eager to learn and had mastered the basic commands of sit, stay, come and off--as in "off" the couch "off " the bed. A few times she growled at my husband and at my daughter. Both instances were over a toy she thought she needed to hover over and guard. I received some advice to gently but firmly take her face in my hands and look her straight in the eye and tell her "no", when this unacceptable behavior was exhibited. After a few weeks she didn't do it any more.

I find it strange that she is such a loving dog to the kids and anyone else that comes over. She even submissively urinates when someone new comes over to meet her. She runs up to them and begs to be petted and the minute they do she urinates.

Is that strange to have a dog submissive in one sense and now acting aggressive towards the children? Every morning when my son waits for the school bus I take the dog out on her leash and we wait with him. It is a ritual. This morning when my son went to put her leash on her collar she growled at him. I told her "no" and then held her collar myself and told my son to try to put her leash on again. The dog growled at him. I firmly said "no" and she quit. She respects my authority with no question but what do I do about the children now? The last thing I want is a cranky Mastiff. I appreciate any advice you have to offer.

A: This is a serious situation. She is likely trying to put the children under her protection. It's a noble concept, but in nature it means snapping at the little ones to keep them in line, so she can get them behind her and face danger in front of them. They are not pups, so their skin is not thick enough for her to snap them. They also won't be able to duck out of the way as a pup would do. Her behavior is instinctive, perhaps even noble, but it must be modified for everyone's safety.

If you got this dog from a responsible breeder, speak to that person about this. It truly is a threat to your dog's survival, and the breeder needs a chance to try to help. Also, ask your veterinarian if he or she can recommend a behavior specialist in the area. With three children so young, and a dog so huge, you really need in-person help, right way on this.

Dominance has to be used carefully in a situation where the dog is dominating those under her. When you "model" alpha behavior for a dog, you give her an example of how to be a leader. The dog may then turn around and use it on those she perceives as being under her--in this case, your kids. So, the exact way you handle this dog is extremely important.

The rougher a dog is handled (mentally or physically), the rougher that dog may try to be with those the dog sees as being under her in the pack. With such a size and strength difference between the dog and your young children, there is little margin for error here. The dog also needs to be expertly evaluated to see if she is suited for a home with young children. Some dogs simply aren't.

Mastiffs are generally stable dogs, and hopefully this can be worked out with behavior modification. Do keep up the 100% supervision of any dog with your kids, until the kids are at least school age. That is very wise of you.