marking certain spots

Question
We have a unnurtured boston terrier, and we don't want to.  I have heard it looses character.  Our terrier is 18 months old, but just a few months ago we discovered his 3 spots where he regularly urinates, that we have not seen prior.  We tried to spray all the spots with some enzyme spray, we tried to keep the dog outside more, and have long walks and rewarding with treat everytime he urinates.  Two of the spots were tables, another one is a statue, and were brought outside to clean up, stood there for a week, and as soon as we brought it back inside, the dog somehow sneaked away, and did the same.  Please help we will try anything.  Thank you.

Answer
You may not like my response, but if you are not going to show your dog in the breed ring, or breed him responsibly (key word - responsibly), then you are making an error by not neutering him.  Neutering a male dog does NOT change his character, although it will certainly minimize the potential for dog to dog aggression.  It will also prevent testicular cancer later in his life, and would have prevented the urine-marking problem you now seem to be experiencing.  If your puppy was previously house trained, then the marking of vertical objects sounds like he has simply reached maturity, and is now "telling" everyone where his territory is.
If the dog is urine-marking, neutering may be your only hope to stop it, although some dogs don't stop even afterward.  
Frankly, your attitude about neutering is a bit old-fashioned and not based in any facts.  The most important reason for doing it is to prevent yet another unwanted litter of puppies.  If you think that leaving a dog unneutered is ok, pay a visit to your local animal shelter, or go to this website and look around: www.dogsindanger.com.
Millions of homeless pups and dogs are euthanized every year - don't contribute, even accidentally, to that problem.