help with my male dog

Question
My male dog wont stop spraying? he is a male chihuahua, he is 4 years old, his diet is purina inside small bites, he is nutered but was not nutered untill 2 years old. He breed several times. He is an inside dog only. I do let him out only to use the potty about 4 times a day. He has been spraying since he was a puppy. I am at my wits end. I have spent alot of money on him and now im gonna lose my mind. I've potty trained him and my female they go out often and I also have pee pee pads down daily. They both are very well potty trained but he sprays daily. I have tryed spanking his bottom, doesn't work. I also tried the mark out wraps he just pees on them, he doesn't mind peeing on him self. i've tried to cage him but he screams none stop ,that would not be so bad but he tears at the cage trying to kill him self he rips his nose and face untill theres blood every where. i dont know what to do any more i've tried the zap collars and ultra sonice stuff. this ones really stuborne. all i want to do is stop him from spraying, it's like he must know. I have now resorted to locking both dogs in the bathroom, when not at home. that works but it seems over night when I'm a sleep he sprays. I need serioius help please. any help you can give would be greatly appreciated
                                                                                 Thanks Zara  

Answer
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/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm

I frankly don't know if at his age obedience training will be enough.  I hate to suggest drugs from the vet or or older, harsh methods, but am not sure what else to do.  

Catching him in the act of marking calls for stronger corrections than the otherwise effective "Bad dog!".  When it misbehaves, throw it on its back, and growl "Bad dog!" right in its face.  Hold it down until it lifts one back leg to show submission.   You can pick him up with your hands behind his front shoulders and hold him up with his back to you.  Keeping him far enough away to keep his head from smashing into your face, hold him until he stops struggling and relaxes.   Others like the squirt bottle.  Fill it with water and a little vinegar or lemon juice.  Give it a squirt in the face as soon as it misbehaves.  Dogs hate that.