Jack Russel Aggression

Question
My girlfriend and I rescued a 3 year old JRT.  We've had him about 1 month and he is a great dog.  He is very well trained and listens to both of us.  The other night I tried to slide him over in bed and he got very angry, biting growling and very aggressive.  We made him sleep on the floor that night.  Since then he has been almost scared of me.  He still minds me but he's just not acting the same.  this morning he rolled over on his back so I could pet his stomach but thenafter petting him a bit he sarted growling and tried to bite me.  I told him NO and made him stop and then put him outside for awhile.  He puts up with me but I cna tell he's not happy and tucks his tail when he's around me.  He hasn't done this to my girlfriend.  I'm worried because he goes from being just fine to very aggressive and biting instantly with no warning.

Answer
Hi Steve,
Being a rescue dog, you just don't know what kind of environment he came from. I suspect the previous owners were probably a little abusive (if there is such a thing as a "little" abusive).  When you corrected him he probably had bad memories of the previous owner and got nervous, which is why he is acting afraid. They don't forget very easily.  However, you certainly can't have him growling and aggressive to you AT ALL. The MINUTE he senses that you or your girlfriend are nervous, he will act on it and try to take control of the situation. The best thing you can do it try to provide a very strict routine for him with no deviations. Take him out on a regular basis to expend some energy - it also curbs aggression - feed him at the same time every day and put him in his crate to sleep. Whatever you do, don't be wishy washy, he needs a strong and firm hand but not an abusive one. Consistency and them knowing what to expect at all times is a great teaching and training tool. I strongly suggest taking him to a dog training school (NOT PETCO or PETSMART), a "real" dog school where you can both learn the proper way to handle and deal with any areas of aggression. He's still young enough that you can get a handle on it and turn him around. If you do nothing, he will continue to test you and get more aggressive. It sounds like he has attached to your girlfriend and is in protective mode - not allowing anyone else easy access to her. This can become a real problem so get to the training and nip it in the bud right away.
Good luck with him