The first question - is your dog neutered? I'll bet NOT! He has reached sexual maturity and wants to be the Alpha male.
Staffordshire Terrier is a nice, fancy name for Pit Bull. Bullies that have not been through obedience and socialization and those whose owner think wrestling and playing tug-of-war with them, are the ones who give the breed a bad rap.
Get your dog neutered! No excuses, just do it! It should help reduce some of his sexual drive and dominance. He will be most likely be a happier, less aggressive, less frustrated dog.
Get yourself and your dog into an obedience class. He needs to trust and respect YOU and your commands!
Go to http://ezinearticles.com/?expert=Karen_Soukiasian
You will find a number of articles which you should find helpful.
Good luck!