Since we had our staffy 7 weeks ago I have been doing lots of research on dogs behaviour, etc.
Try reading Jan Fennell - The Dog Listener and if you have Sky, watch Cesar Millan - The Dog Whisperer on Sky Three at 6pm. They basically use the idea that dogs are pack animals and therefore you need to show them you are the leader of the pack and the reason they do certain things is because they believe they are leaders and not you.
When we go out we put our 8 month old staffy in the kitchen and remove anything that she can chew because the first few times we left her she demolished two pairs of shoes. I have also forgotten to take my slippers out twice and shes had them too, even though she has several toys and hide bones to chew on of her own. She can also jump up on to the table so everything comes off there too, and she is fine when we do this. We also leave the radio on for her. We were going to try her with a cage too when she first chewed our shoes, but we didn't need to as long as we removed any chewables out of her reach when we went out. She definitely is better when the radio is left on as the house goes all quiet when you go out. We give her a couple of treats on her bed to occupy her mind as we leave and don't speak to her or give eye contact immediately before going out, sounds harsh but works, and never leave food for them to eat whilst you are out.
Staffy's are big chewers and can get bored easily so they need lots of exercise, stimulation and plenty of toys to chew.
She really needs a minimum of an hours walk a day preferably more.
Hope this helps you.