behaviour in 17mth old german shepherd

Question
hi,my 17 mth female shepherd seems to be getting very territorial in the home and out. can they go through a "phase" at this age,she is normally very good off lead at recalls etc,still is but seems to want to chase other dogs more, and runs up to certain people (or a pushchair the other day) barking,she comes back,but has made me wary.Can this be normal (i know not acceptable)at this age,due to have her spayed in oct.many thanks.

Answer
It is not a phase, but maturing.  She is a big girl now and ready to claim and defend a territory.  Spaying should help, but you need to give her stronger leadership.   The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/