Marking?

Question
My 1 yr old Choc Lab has a habit of pooping whenever we go to new/different place (anywhere but home).  If I take him for a walk down the street, he has to drop one when we get out of his normal 'range'.  When we go to the kids' soccer games, on a hike, swimming, etc...he gets very excited, sniffs everything, pees (this part I can deal with) and then has to poop.  Even just a tiny bit.  He does this even if he has just 'emptied' in an acceptable place moments before.
I've tried tugging the leash and telling him 'no' and he stops but I can tell he's gonna drop one at any minute...and he does.
My vet says he's just marking territory but this habit stinks!  It's not pleasant for me and others around him and it's a pain to clean up.  I'm getting to the point that I don't want to take him w/ me because of it.  I love my dog but this needs to stop.
Any advice?
thanks

Answer
I don't have much better idea on stopping him than your vet.  If he isn't neutered, doing so might help some.  It is no cure all.  If you can keep him moving rather than stopping to sniff, it may help.  They do have to find the right place.  Once they have stopped and have their back humped up, there is little stopping it.  

I can help some with cleaning up after him.  One of the best ways is to carry plastic bags with you. Old bread wrappers will do.  Put one over your hand, pick the stuff up, and turn the bag inside out.  Tie a knot in the top and deposit it somewhere suitable.  I try to avoid trash cans next to picnic tables.  My daughter actually has a small container of plastic bags mounted on her dog's leash.  I also make up French fry like containers out of old cardboard boxes.  Along with another square of cardboard to scrape it in, and put it in a heavy zip lock bag.  You can then tuck it in your pocket until you come to somewhere to dump it.  

If you are feeding one of the premium, concentrated chows, they tend to produce smaller, firmer stools that are easier to clean up.  That is one of the real advantages to the more expensive chows.  I don't think the dogs care that much. I am afraid most Labs would prefer the cheap stuff they get to eat more of.  sticking to his chow and little else reduces the tendency toward loose, hard to clean up bowel movements.