Hi,
Shouting and smacking his bum all be it with a newspaper will get you nowhere! He is showing himself to be dominant and as you have seen he completely ignores negative behaviour from you and to be honest if he has a strong will he may very well turn around and give you a good nip or even a bite if you continue to show him negative behaviour.
Any good trainer will train any type of dog no matter how stubborn or dominant with their voice and eye contact, with constistancy, calmness and repetitive commands...... that truly is all that you need, if you can not control a dog with those means alone it means he certainly does not see you as someone with an air of authority so he will most definitely stand up to you as an adult in the worst possible way, if you are to shout and smack him.
Not everyone has an air or authority, in the home, we can bring in techiques like segregation, which to a dog is one of the worst punishments, to be removed from their family and put somewhere alone for a little while, so if he refuses to obey your commands you pop him in the kitchen, the garden, the dinning room on his own for 10 minutes then allow him to come out and try your command again.
Outside he is coming up to and of an age now where he will be at his most stubborn anyway, it is his age and his own instincts are leading him astray, he needs as already said to be put on a long line, his recall will be at it's weakest for the next few months, and quite rightly as you have deduced he is on his way to having a good telling off or even a bite or fight if he goes around humping other dogs, so the long line will keep him in check here too and protect him from his own behaviour. Putting your dog on a long line is better than a flexi lead as it gives him a lot of freedom and the minute he thinks he can run off, or hump another dog you can reel him in immediately.
If he
is off lead and will not recall, when he does eventually come back, you may feel like punishing him, i.e a good telling off, it can be very frustrating, but bite your tongue, it is the worst thing to do, you must praise him.
Continue to praise him everytime he does something right, but above all else practise keeping a strong, stern, calm voice and strong eye contact you need to establish yourself as his master and repeat and repeat what you wish him to do until he does it.
Remember you are in control of him and you must not let him get away with anything, he will learn from positive reactions 100 times more than a negative one.

Good luck.