pamperring

There are lots of reasons why dogs behavior changes. Sometimes dogs see themselves as the alpha - the leader. And in that case they feel they have every right to do what they want and act like other people and dogs are lower than they are. If it's food aggression or possessiveness you'll have to work on training them. Show them that the more they share the more treats and praise they will get. If it's people possessiveness then the best thing to do is show them it's not tolerated by leaving the room (if they are possessive of you). My little chihuahua has started to show a few traits. when she's on my or my husbands laps or being held by us she growls at any dog who gets near. She just started this - she's only 4 years old. so what i do is say 'bad dog' and put her down immediately and leave or turn my back. That way she realizes being nasty to other dogs gets her human to ignore her and that's probably the best type of punishment to give a dog. There's a fantastic show on Animal Planet called "it's me or the dog" i get a lot of training tips and ideas from watching that show. all about positive re-inforcement (not punishments)