Separation Anxiety???

Question
I have a 3 year old bichon shitzu. We got him from a friend who breeds them and he was the last puppy to go so we got him at about 3 months old. We have had problems house training him from day one since the breeder lets her puppies pee on carpet squares that were placed around her house. So I am assuming he thought all carpeted areas we free game. He finally stopped peeing in the house around 1 year old. We have a 18 month daughter now and I am pregnant again. Just recently (within the last month or so) everytime I leave the house and do not bring him with he will lift his leg around the house. Today for example, I left the house at about 10:30 (I let him outside multiple times before leaving) and I got home at 12:30. When I got home there were 3 places where he had peed. He will not do this while we are home. Is he mad at me for leaving the house without him or should I be concerned about something medical. Any suggestions on how to stop it?

Answer
I can't comment on his medical condition, if any; you need a veterinary consult for that.  If your dog is not neutered, do it.  Unfortunately at age 3, some of his testosterone related behaviors (this includes marking, which is what he's doing) may remain, but it can't hurt to neuter him and will make his life calmer.  This sounds like the dog is marking as a method to "assist" you to find your way back.  It's also possible your elevated hormones are provoking his concern: dogs do "know" when a female human is in estrus or pregnant, just as dogs can indicate occult illness in humans.  

"Letting" the dog out isn't going to teach him that what he does out there is rewarded.  You have to TAKE him out, every time for the next few weeks, observe his urination, praise and offer tiny food treat when he urinates (praise as he's doing it, offer treat immediately after).  Once you absolutely know the dog has urinated, confine him before leaving the house.  The kitchen with strong baby gate (you most likely have a couple!), soft bed, water and interesting toy, such as the Buster Cube (which dispenses a portion of his daily meals as he rolls it along, keeping him very occupied) will help divert his attention from his apparent insecurity regarding your absence.  IF you find a puddle in the kitchen, do NOT yell at him or in any way show ANY reaction.  Wait until he's out of the room and clean it up with enzyme products intended to remove scent of urine (as much as is possible), not products containing ammonia (which is an ingredient of urine).  Be patient: your efforts at re-training him will most likely not require more than a few weeks.

About ten minutes before leaving the house, confine the dog (as described above) and then ignore him.  You can randomly confine him for a few minutes at a time throughout the day and then let him out with a "good dog" pat so he doesn't perceive confinement as a prelude to your leave taking.  Don't say 'goodbye' to the dog or make any comment, just leave.  When you return, greet him calmly, no huge display just a nice pat, after a few seconds of your reentry to the house.  Feed him both his meals (every dog should be fed twice daily) in the confinement area; this will help to motivate him not to eliminate there.  If the kitchen isn't convenient, use a bathroom with a window, but don't close the door: use a gate.  Give this treatment about three weeks; if the dog hasn't begun to improve, or if his separation becomes worse, use followup feature to this original question.