Keep him attached to you at all times, and don't give him an opportunity to do anything you don't like.
When you're home, attach a leash to your belt ("umbilical" training method) and that way you'll know when he's getting ready to wee, and you can shout out sharply, and rush outside, praise for going outside. Walk him by your staffie nonchalantly, and the second he gets ready to mount, sharply correct. He just needs to understand the rules. It takes time, and will change your lifestyle completely for a month or so, but it is WELL WORTH it when you have a well-behaved dog that can be trusted at all times.
I have had intact males that never were fixed and never wee'd in the house or mounted other dogs after using this training method.